taxonID	type	description	language	source
03EF87FEFFA2FFC2FC6DFDCAFAA8F9F9.taxon	description	(Figs 1, 2; Table 4) Korshunova et al. 2017 a: 72 – 4, supplementary materials. Diagnosis: Body narrow. Notal edge completely reduced. Cerata non-elevated, few per row. Ceratal rows simple. Rhinophores smooth. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of denticles. Radula formula 0.1.0. Central teeth usually with distinct cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens usually short, prostate indistinct. Supplementary gland present, inserts to penis. Massive external permanent penial collar absent. Penis internal, narrow, armed with a hollow, well-defined stylet. Genera included: Abronica Cella et al., 2016. Remarks: The family Abronicidae invariably represents an earlier off-shoot of Fionoidea evolutionary radiation, and is placed even more basally than the triserial Eubranchidae, as sister to all other families of the superfamily Fionoidea, according to the molecular phylogenetic data (Figs 1, 2). However, at the morphological level, the family Abronicidae is similar to the distantly related family, Trinchesiidae, in having a uniserial radula and a reduced slender body with a fewer number of ceratal rows. Such a remarkable mosaicism at different organismal levels is an indispensable feature of biological evolution. All the substantial diversity caused by many various processes, including the reduction of some characters, as well as the progressive development of other features (see details in: Korshunova et al. 2021, Martynov et al. 2022), forms an astonishingly diverse perspective of the organism, which must be correspondingly reflected in a taxonomic system, instead of greatly obscured by pan-lumping incorrectly named ‘ intermediate forms’ and ‘ variations’.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF96FFE9FEF2FB80FE5BF91C.taxon	description	(Figs 1, 2; Table 4) Gray 1827: pl. 3, figs 16 – 19. Korshunova et al. 2017 a: supplementary materials. Diagnosis: Body broad to narrow. Notal edge completely reduced in majority of genera. Ceratal rows simple or arched, numerous non-elevated cerata per row. Rhinophores smooth, perfoliate, or papillate. Anus commonly cleioproctic, rarely pleuroproctic. Masticatory edges of jaws commonly smooth, but can also be moderately denticulated with single row of denticles. Radula formula 0.1.0. Central teeth arc-shaped, pectinate. Commonly proximal receptaculum seminis. Vas deferens moderately long to very long, prostate indistinct to moderately distinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, narrow or broad, unarmed. Genera included: Aeolidia Cuvier, 1798, Aeolidiella Bergh, 1867, Aeolidiopsis Pruvot-Fol, 1956, Anteaeolidiella M. C. Miller, 2001, Baeolidia Bergh, 1888, Berghia Trinchese, 1877, Bulbaeolidia Carmona, Pola et al., 2013, Cerberilla Bergh, 1873, Limenandra Haefelfinger and Stamm, 1958, Spurilla Bergh, 1864, and Zeusia Korshunova et al., 2017. Remarks: One of the two oldest families within the suborder Aeolidacea, Aeolidiidae Gray, 1827 at the diagnostic level is well characterized by the presence of a cleioproctic anus in combination with broad, arc-shaped, pectinate radular teeth, but the deep-sea genus Zeusia Korshunova et al., 2017, which evolutionarily is sister to the type genus of the family, Aeolidia, was proved as having a well-defined pleuroproctic anus (Korshunova et al. 2017 d). This fact that arc-shaped, pectinate radular teeth occur not only within the familiesFacelinidae (genus Burnaia Miller, 2001) andPleurolidiidae, which are related to Aeolidiidae, but also within the very distantly related families Xenocratenidae and Trinchesiidae (genus Trinchesia Ihering, 1879 in narrow sense, see above), and understanding that pleuroproctic anus is an ancestral feature, in some form preserved at least in a few genera in a majority of the Aeolidacean superfamilies and families (e. g. even within the superfamily Fionoidea with a predominantly acleioproctic anus, there is a family Murmaniidae, in which, as a rarest exception, the pleuroproctic anus has been documented; Martynov 2006; Tables 3, 4), an overlumping approach has the potential to dismantle the entire family-level taxonomic structure within the suborder Aeolidacea, and place every species into a single family Aeolidiidae Gray, 1827, or Glaucidae Gray, 1827. Therefore, to prevent this, fine-scale morphological differentiation in combination with molecular data (Synopsis; Figs 1, 2; Tables 3, 4) must be applied regardless of whether the outcome results in species that are ‘ easily characterized and recognized by the general public’ or not. To say that one must lump species into a single genus (e. g. Kim et al. 2024) so that it will be easier to identify nudibranchs in the field truly hinders the quest for knowledge that is the purpose of public scientific inquiry. A particular case, related to the family Aeolidiidae, needs to be specially addressed. A family, Magallanidae, has been described recently by Ortea and Moro (2020) in an unusual manner. First, in the same paper, a new species, Aeolidiopsis elcanoi (Ortea and Moro 2020: 16 – 24), was described within an old genus, Aeolidiopsis, and the new species initially was placed unambiguously in the family Aeolidiidae (Ortea and Moro 2020: 16). However, at the end of the description of the new species Aeolidiopsis elcanoi (Ortea and Moro 2020: 24), it was assigned to a new genus Magallanes and a new family Magallanidae, very unusual for common taxonomic works; thus, its taxonomic position was presented in the same paper two times using two different sets of families and genera (Ortea and Moro 2020: 24). Aeolidiopsis / Magallanes elcanoi possesses broad, arc-shaped, pectinated central teeth, a reproductive system with a relatively long vas deferens without a supplementary gland, and rather flattened cerata. All these characters are consistent with the current family Aeolidiidae, even taking into consideration our major principle of fine-scale taxonomy as consistently employed in the present study. Molecular data are not available for this taxon, although according to morphological data the genus Magallanes and the family Magallanidae are probably a part of the intrageneric diversity of the family Aeolidiidae (and, therefore, Magallanidae are not listed separately in the synopsis and Tables 3, 4), we refrain from its synonymy with Aeolidiidae, because with more data, Magallanidae may potentially contribute to a further fine-scale differentiation within Aeolidiidae, which is still partly heterogeneous and contains morphologically considerably different taxa. Superfamily Flabellinopsoidea Korshunova et al., 2017, herein established (Figs 1, 2; Tables 1 – 3) Diagnosis: Aeolidacean superfamily with triserial and uniserial radula. Body relatively wide to narrow. Notal edge discontinuous. Cerata on broad flap-like extensions, numerous per row. Ceratal rows branched. Rhinophores perfoliate, granulated to smooth. Anus pleuroproctic. Anterior foot corners present. Elaborate oral glands absent or present. Masticatory edges of jaws bear several rows of compound, sharpened or tubercle-like denticles. Central teeth usually with cusp compressed by adjacent lateral denticles. Lateral teeth narrow or with attenuated process basally, denticulated, smooth, or completely absent. Distal receptaculum seminis or proximal receptaculum also present. Clasping organ in female part of reproductive system absent. Vas deferens long, with distinct or indistinct prostate. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, unarmed or armed with stylet. Families included: Flabellinopsidae Korshunova et al., 2017 and Hantazuidae fam. nov .. Remarks: The families Flabellinopsidae Korshunova et al., 2017 and Hantazuidae fam. nov., although internally completely disparate regarding such key family-level aeolidacean characters as the presence of a triserial or uniserial radula, as well as the absence or presence of a distinct hollow cuticular penial stylet (see Synopsis below), robustly align as sister to each other according to molecular phylogenetic analysis (Figs 1, 2), and in turn are sister to the families Paracoryphellidae, Flabellinidae, and Coryphellidae, however, with lower support (Figs 1, 2). Although previously the family Flabellinopsidae was also placed as sister to Paracoryphellidae, Flabellinidae, and Coryphellidae (Korshunova et al. 2017 a), in some other analyses it is more distantly related to Flabellinidae (Karmeinski et al. 2021), or even as sister to Notaeolidiidae (Goodheart et al. 2018), which definitely possess a very different, ancestral oligoserial radula. Despite that, in our phylogenies with a maximally possible (at that time) broad taxon sampling (Korshunova et al. 2017 a), Flabellinopsidae invariably aligned as sister to Paracoryphellidae, Flabellinidae, and Coryphellidae. The previous results (Goodheart et al. 2018, Karmeinski et al. 2021), and relatively low support in the present study (Figs 1, 2), justified the separation of Flabellinopsidae Korshunova et al., 2017 and Hantazuidae fam. nov. into a separate superfamily Flabellinopsoidea Korshunova et al., 2017, established herein (see Synopsis below; Figs 1, 2; Tables 1 – 4). In further support of this, despite that Flabellinopsidae Korshunova et al., 2017 and Hantazuidae fam. nov. internally are drastically different to a maximal degree, externally they show some similarity in the presence of flap-like, notal-derived ceratal bases (MacFarland 1966, present study, see Synopsis below) instead of merely discontinuous notal edge or stalk-like ceratal bases as in the superfamily Flabellinoidea (Korshunova et al. 2017 a), which thus morphologically justifies the separation of the superfamily Flabellinopsoidea (Figs 1, 2).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF93FFF5FC67FDDAFEC7FC7E.taxon	description	(Fig. 2; Tables 1 – 3) ‘ Tribe Cleioprocta’ part. Odhner 1939: 50 – 3. Diagnosis: Aeolidacean superfamily with uniserial radula. Notal edge commonly completely reduced, rarely present, significantly reduced. Cerata commonly placed in various regular rows and other regular patterns, such an arcs or horseshoe-like structures, often in combination with linear rows. Anus commonly cleioproctic, rarely pleuroproctic or acleioproctic. Anterior foot corners commonly present. Elaborate oral glands absent or present. Masticatory edges of jaws in many taxa bear a single row of denticles, in some taxa smooth. Both proximal and distal seminal receptaculums are commonly present, more rarely reduced to single one. Clasping organ in female part of reproductive system absent. Vas deferens commonly moderately long, prostate indistinct or distinct. Supplementary gland is invariably absent, but accessory glands may be present in several taxa. Massive external permanent penial collar absent. Penis internal, can be very simple, conical or highly elaborated with massive penis with various warts and folds, sometimes with hollow stylet or other cuticular structures. Families included: Favorinidae Bergh, 1899, reinstated, Glaucidae Gray, 1827, Facelinidae Bergh, 1899, Babakinidae Roller 1973, Pleurolidiidae Burn, 1966, Myrrhinidae Bergh, 1905, and Aeolidiidae Gray, 1827. Remarks: The superfamily Aeolidioidea represents a well-defined taxonomic unit, well supported by molecular phylogenetic data (Figs 1, 2), with an exclusively uniserial radula and predominantly cleioproctic anus (despite the rare presence of pleuroproctic and acleioproctic ones), and commonly completely reduced notal edge, also with some rare exceptions. The cerata tend to form distinct rows or arches of various shapes, rarely continuous. A special supplementary gland in the male reproductive system is completely absent, but various accessory glands may present. The superfamily Chudoidea superfam. nov. and family Chudidae fam. nov. may be sister to the superfamilies Aeolidioidea, Flabellinopsoidea, and Flabellinoidea with low support (Fig. 2), which may indicate a potential triserial common ancestor for the otherwise uniserial Aeolidioidea (see Tables 1, 2). The taxonomic volume of the superfamily Aeolidioidea is lateral posterior teeth, SEM. M, radular teeth, details of anterior-most central tooth, SEM. N, details of the right anterior side of the body showing common genital opening in an elevation under the distinct regular ceratal rows. O, scheme of reproductive system. Scale bars: F, 300 μm; G, 300 μm; H, 300 μm; I, 100 μm; J, 30 μm; K, 30 μm; L, 300 μm; M, 100 μm; O, 0.5 mm. Photos and SEM images: Alexander Martynov. Abbreviations: a, ampulla; fgm, female gland mass; pr, prostate; psh, penial sheath; rsd, receptaculum seminis distal; vd, vas deferens. restricted here [the obviously non-aeolidioidean families, such as Notaeolidiidae, Flabellinopsidae, and Flabellinidae, as currently assigned in WoRMS (2024), as well as any other potential families are removed] only to the core monophyletic group of uniserial families, which includes the families Favorinidae Bergh, 1899, reinstated, Glaucidae Gray, 1827, Facelinidae Bergh, 1899, Babakinidae Roller, 1973, Pleurolidiidae Burn, 1966, Myrrhinidae Bergh, 1905, and Aeolidiidae Gray, 1827, but not several other families distantly related to Aeolidioidea, as are incorrectly currently listed in WoRMS (2024). A genus Zatteria was established by Eliot (1902) from the Indian Ocean, and despite it never being redescribed since then, from the time of the original description, it was placed as an addition (McDonald 2009) to the taxa, which is currently included in the superfamily Fionoidea. However, the combination of the very large size of Zatteria (up to 8 cm), partly perfoliate rhinophores, short uniserial radula with central tooth with distinctly protruding cusp, and few lateral denticles, and no armature in the reproductive apparatus, point rather to the superfamily Aeolidioidea, potentially as some aberrant genus of Facelinidae or Myrrhinidae. See other parts of the Synopsis above and below for their proper superfamily placement.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFACFFCCFF39FE74FC38FCBB.taxon	description	(Figs 1, 2; Table 4) ‘ Genus Flabellina sensu latissimo ’ Gosliner and Griffiths 1981: 105, 109 – 15.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFACFFCCFF39FE74FC38FCBB.taxon	diagnosis	Diagnosis: Body moderately narrow. Notal edge completely reduced. Cerata in separate rows, on elevations, numerous per row. Ceratal rows partly branched. Rhinophores perfoliate. Anus mixed (pleuroproctic in a higher acleioproctic position). Jaws with masticatory edges bear several moderate denticles, tuberculate to more sharpened. Radula formula 1.1.1. Central teeth cusp compressed by adjacent lateral denticles. Lateral teeth smooth with moderately attenuated process basally. Distal receptaculum seminis. Vas deferens moderately long, prostate relatively distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Apata Korshunova et al., 2017 and? Tularia Burn, 1966.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFACFFCCFF39FE74FC38FCBB.taxon	diagnosis	Diagnosis: Aeolidacean superfamily with uniserial radula. Notal edge completely reduced. Cerata on indistinct elevations or low stalks. Ceratal rows branched to simple. Rhinophores smooth. Anus pleuroproctic or mixed in a higher acleioproctic position. Anterior foot corners present. Elaborate oral glands commonly present. Jaws with masticatory edges bear a single or several irregular to distinctly sharpened, elongate denticles. Central teeth with non-compressed cusp. Distal and proximal receptaculum seminis or only a proximal receptaculum. Clasping organ in female part of reproductive system absent. Vas deferens moderately long to short, prostate distinct. Supplementary gland absent. Accessory gland absent or, rarely present. Massive external permanent penial collar absent. Penis internal, not considerably widened, armed or unarmed. Families included: Unidentiidae Millen and Hermosillo, 2012. Remarks: Family Unidentiidae in the present study is sister to the superfamily Fionoidea, although not with the highest support (Figs 1, 2). In other phylogenies Unidentiidae also never nested unequivocally with any of the known Aeolidacean families (see: Korshunova et al. 2017 a, 2019 b, Karmeinsky et al. 2021, present study; Figs 1, 2). Consistent with the molecular data, morphologically, Unidentiidae represent a bizarre combination of several traits that otherwise can be mosaically found within all three major Aeolidacean superfamilies, Fionoidea, Aeolidioidea, and Flabellinoidea: uniserial radula, reduced notal edge, but at the same time cerata on elevations or low stalks, and a pleuroproctic to higher acleioproctic anus, complemented with the absence of a supplementary gland, but very rarely the presence of a not-well documented accessory gland. Even taxonomically this unusual family, which externally may simultaneously look like ‘ a flabellinid’ or a ‘ facelinid’, has been highlighted as having features of several, otherwise distantly related superfamilies and its representatives were initially called ‘ Flabellina ’ sensu latissimo (Gosliner 2010), but finally were assigned to a completely separate family, remarkably in the molecular era, using only morphological argumentation (Millen and Hermosillo 2012). Taking into consideration that Unidentiidae never place consistently into any of the Aeolidacean superfamilies, the separate superfamily status for Unidentioidea, herein established, is highly justified.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF97FFF7FC35FEB0FB3BFCCE.taxon	description	(Figs 1, 2; Table 4) Roller 1973: 117 – 8. Diagnosis: Body moderate to narrow. Notal edge present, partly reduced. Ceratal rows branched-to-simple, not clustered, numerous non-elevated cerata per row. Rhinophores perfoliate. Anus pleuroproctic. Masticatory edges of jaws moderately denticulated with several rows of tubercle-like to partly sharpened denticles. Radula formula 0.1.0. Central teeth with compressed cusp. Distal and proximal receptaculum seminis. Vas deferens moderately long, with mostly indistinct prostate. Accessory gland present. Massive external permanent penial collar absent. Penis internal, relatively narrow, basically conical in various proportions, unarmed. Genera included: Babakina Roller, 1973.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF9FF99FF58FC8EFB29F9C8.taxon	description	(Figs 1, 2, 13; Table 5) Korshunova et al. 2017 a: 27. Korshunova et al. 2017 b: 140. Type species: Coryphella nobilis Verrill, 1880. Diagnosis: Body moderately wide. Notal edge present, continuous. Cerata in continuous rows. Rhinophores wrinkled. Anterior foot corners present. Central teeth with narrow cusp compressed in different degrees with distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Moderately long vas deferens, distinct prostate in several loops expanding into narrow, long, penial sheath. Penis narrow, tubular. Species included: Borealea nobilis (Verrill, 1880) comb. nov. and Borealea sanamyanae Korshunova et al., 2017 comb. nov .. Remarks: Eleven Borealea nobilis and six Borealea sanamyanae formed separate sister-clades (PP = 1, BS = 100), within the common genus Borealea clade (Fig. 13). The Borealea clade had the sister-position to the clade Coryphella, but not with high support (PP = 0.98, BS = 71; Fig. 13). The genus Borealea immediately differs from the sister-genus Coryphella by its continuous notal edge, narrow cusp of the central teeth compressed (in various degrees), lateral teeth with attenuated basal process, and non-discoid penis (Korshunova et al. 2017 a, present study). All these differences were incorrectly dismissed in Ekimova et al. (2022), but two years later, in 2024, all three species of Borealea (so far known) formed a distinct clade in Ekimova et al. (2024). In other words, the trees’ topology returned the results published in Korshunova et al. (2017 a). The genus Borealea also forms a distinct clade according to the present molecular phylogenetic analysis (Figs 1, 2, 13). Kuzirian (1977) exhaustively studied the morphological, ecological, and nomenclatural data on Borealea nobilis based on numerous specimens collected close to the type locality. Among other details, Kuzirian (1977: 233, fig. 6) unequivocally stated that the ‘ penial sac contains a large expandable preputium and the long narrow tubular penis’. However, Ekimova et al. (2022) described a broad penial sheath and lobe-shaped penis. Taking into consideration the exhaustive details and high methodological approach in Kuzirian (1977), we conclude that the penis of ‘ Borealea nobilis ’ in Ekimova et al. (2022) was incorrectly described. Moreover, an immediately recognizable morphological feature of the genus Borealea, the compressed cusp of the central teeth (the cusp of the central teeth of Borealea, even in various degrees of compression, are readily recognizable compared to the sister-genus of Coryphella proper with distinctly non-compressed cusps in all three species) were clearly and unambiguously depicted in Ekimova et al. (2024: fig 9) for all three species of the distinct Borealea clade. While the valid genus Borealea was incorrectly synonymized based on incorrectly assessed paraphyly (see details above in the Results) two years ago in Ekimova et al. (2022), the illustrations of radula patterns in Ekimova et al. (2024: fig. 4) clearly show morphological differences between the radulae of the group that includes nobilis, sp. 1, and sanamyanae and of all other ‘ Coryphella ’ with a non-compressed cusp yet there was no mention of ‘ paraphyly’ in 2024 and no indication that a new genus was necessary for the group with a compressed central tooth, not to mention that a valid genus had previously been described in Korshunova et al. (2017 a) for that group. Lumping genera based on incorrect analysis and then failing to acknowledge the error, even when providing illustrations showing morphological distinctness, shows a bias toward lumping rather than a desire to follow the mosaic patterns of evolution to their fine-scale taxonomic conclusions. Remarkably, the incorrect synonymization of the genus Borealea with ‘ Coryphella ’ further concealed the existence of (and still not properly described) hidden diversity among the true Borealea, since an undescribed species, sister to B. nobilis, was mentioned in Ekimova et al. (2024). In the present study we, for the first time, report the discovery of B. sanamyanae (initially discovered in the north-west Pacific, Korshunova et al. 2017 a: 27 – 8, fig. 17) from the north-east Pacific (collected in Rich Passage, WA, which also matches a GenBank sequence from British Columbia), which significantly expands the range of the species and genus (Fig. 13), thus further documenting the fine-scale diversity within Borealea. Therefore, the genus Borealea encompasses a broad range of localities in boreal waters of the Northern Hemisphere, but does not penetrate considerably into true Arctic waters. Comparison of the genus Borealea with all valid, currently included Coryphellidae genera is presented in Table 5. See also Results and Discussion.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF98FFF8FF51FF05FD5EF9E1.taxon	description	(Figs 1, 2; Table 4) Iredale and O’Donoghue 1923: 200.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF98FFF8FF51FF05FD5EF9E1.taxon	diagnosis	Diagnosis: Body wide. Notal edge completely reduced. Ceratal rowssimple, numerousnon-elevatedcerataperrow. Rhinophores smooth. Anus absent (unique among members of the entire suborder Aeolidacea) in adult state. Masticatory edges of jaws commonly bear single row of simple denticles. Central teeth without distinct cusp and denticles, individual teeth are mostly fused in a highly peculiar band-like structure, also unique within Aeolidacea, and within a majority of the order Nudibranchia. Distal receptaculum seminis. Vas deferens long, prostate indistinct. Supplementary gland present, inserts into vas deferens. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Calma Alder and Hancock, 1855. Remarks: Whilst all the above-mentioned families of the superfamily Fionoidea possess a unique set of both external and internal characters, the family Calmidae remarkably stands apart even compared to the other otherwise unique families. This is because the family Calmidae possesses two more unique features in both its external and internal morphology: the complete absence of an anus and a very special, mostly fused, radular ribbon comprised of former teeth. This case leaves no room for doubt about the absolute advantage of fine-scale taxonomic differentiation, since if the family Calmidae was lumped into ‘ Fionidae’, then the diagnosis of ‘ Fionidae sensu superlatissimo ’ would include characters barely known even within disparate classes of the phylum Mollusca, and common in a completely different distantly related phylum, Plathyhelminthes, whereas the highly modified, fused radula of Calmidae has very little similarity even to a majority of members of the class Gastropoda. At the same time, phylogenetically Calmidae are sister to the family Cuthonellidae, and, therefore, it is completely impossible to leave the profoundly unique family Calmidae alone and lump all other families into the putative family ‘ Fionidae’. Therefore, by this and all previously presented cases (Korshunova et al. 2017 a, c, 2018, 2021, 2022) of the morphologically highly disparate fionoidean families (Figs 1, 2; Synopsis), we conclude that any further attempts to merge the evolutionary-fuelled diversity of the superfamily Fionoidea into a ‘ single putative family’ must end.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF91FFF3FEDDFB95FD73FEDE.taxon	description	(Figs 1, 2, 6; Table 4) urn: lsid: zoobank. org: act: 0914103 B- 90 B 1 - 49 BB-A 886 - 23 CCAA 961 E 2 C Etymology: The name for the new family and genus is derived from the Russian ‘ chudo ’, which means ‘ amazing thing’ and ‘ miracle’, initially as a reference to the extraordinary set of both external and internal characters in Chudo gen. nov. and Chudidae fam. nov. (Fig. 6) (stem is defined as ‘ Chud- ’), but with the addition of the species’ name ‘ humanistica’ (Latin and Russian for humanism, humanity-adhered) in the binomen Chudo humanistica gen. et sp. nov. it forms a most general meaning as an ideal hope in one of the most difficult times in the world. Diagnosis: Body considerably wide and massive. Notal edge completely reduced, dorsal part of the body smoothly transits to the lateral part. Ceratal rows distinct areas, partly compound, separate, moderate in number, not stalked. Rhinophores smooth to wrinkled. Anus partly mixed — pleuroproctic in a higher cleioproctic position, in an extreme posterior body placement. No elaborate oral glands. Masticatory edges of jaws smooth. Radula formula 1.1.1. Triserial radula is remarkable with very massive lateral teeth. Central teeth square to triangular, with a strong non-compressed cusp. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. Single distal receptaculum seminis present. Vas deferens long, convoluted, prostate non-distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Definite penis not detected. Remarks: The new deep-sea family Chudidae fam. nov. and Chudo humanistica gen. and sp. nov. fundamentally differ from all the nearly 30 currently known aeolidacean families by both external and internal morphological data [see Synopsis of all Aeolidacean families in the present study throughout the text, Korshunova et al. (2017 a), and additionally in Martynov et al. (2019, 2020)], and by molecular phylogenetic data (Figs 1, 2; Tables 1 – 4). After the clarification of the system of aeolidacean superfamilies (see above, after the diagnosis and Remarks to the suborder Aeolidacea), we now present a detailed consideration of the taxonomic placement of the new superfamily Chudoidea superfam. nov. and family Chudidae fam. nov .. In particular, Chudidae fam. nov. differs from any families of the predominantly triserial superfamily Flabellinoidea by the presence of a very broad body with completely reduced notal edge and the presence of distinct, non-continuous ceratal rows (Fig. 6), as well as a partly mixed pleuroproctic in a higher cleioproctic position of the anus, in a remarkably far posterior body placement (such placement is very rare among Aeolidacea, a partially similar condition known mostly within the family Murmaniidae of the superfamily Fionoidea, which is completely different from Chudidae fam. nov. by a number of external and internal features; see Synopsis above) along with the extraordinary patterns of the triserial radula with extremely massive lateral teeth (Fig. 6 F – H). Chudidae fam. nov. differ from any families of the superfamily Aeolidioidea by the presence of a triserial radula, the posterior position of the anus, as well as details of its external features and reproductive system. Chudidae fam. nov. readily differ from an absolute majority of the families of the superfamily Fionoidea by a triserial radula and the absence of a supplementary gland in the male reproductive system. The only family within Fionoidea that possesses a triserial radula is Eubranchidae, which, however, is fundamentally different from Chudidae fam. nov. by the very different shape of its central and lateral teeth. Furthermore, all Eubranchidae possess a reproductive system with a distinct supplementary gland, very different from Chudidae fam. nov .. Ironically, the only family within Fionoidea that does not possess a supplementary gland is the stem-genus bearing family name Fionidae, which, however, differ from Chudidae fam. nov. by the presence of a uniserial radula, the presence of a notal edge, and their general body pattern. From the triserial superfamily Cumanotoidea and family Cumanotidae, Chudidae fam. nov. differ by the distinctly posterior pleuroproctic in a higher cleioproctic position of its anus instead of the acleioproctic position of the anus in the anterior to middle part of the body, the very different general pattern of the radula with massive plate-like lateral teeth instead of hookshaped lateral teeth, by the absence of special clasping structures in the female reproductive system, as well as the absence of a detectable penis. Chudidae fam. nov. differ from the highly paedomorphic family Pseudovermidae (phylogenetically related to Cumanotidae, but morphologically dramatically different) by their completely different body shape, ceratal patterns, anus position, as well as details of the radula and reproductive system. From the uniserial superfamily Unidentioidea and family Unidentiidae, Chudidae fam. nov. fundamentally differ by their general body pattern, patterns of their triserial radula, and details of the reproductive system. Chudidae fam. nov. also differ from two of the basal triserial aeolidacean superfamilies, Apataoidea and Samloidea, by their general body pattern, posterior pleuroproctic to higher cleioproctic anus, and the very different pattern of their triserial radula and reproductive system. Chudidae fam. nov. substantially differ from one of the basal-most aeolidacean superfamily, Notaeolidioidea (unique within the suborder Aeolidacea in that they preserve an oligoserial ancestral radula), by their triserial radula, the absence of a notal edge, the position of the anal opening, and by details of the reproductive system. According to the molecular phylogenetic analysis in the present study, Chudidae fam. nov. are either sister to the superfamilies Aeolidioidea, Flabellinopsoidea, and Flabellinoidea (Figs 1, 2) or sister to superfamilies Cumanotoidea, Flabellinopsoidea, and Flabellinoidea (Fig. 2), although in both cases with low support, which in turn supports the recognition of a separate superfamily, Chudoidea superfam. nov., since this unique new superfamily and family are not directly related to any aeolidacean families so far described (see Synopsis above and below), either from morphological patterns (Fig. 6), or according to the molecular phylogenetic data (Fig. 2). It is important to note that an absolute majority of the taxa within the suborder Aeolidacea possess either a triserial or uniserial radula (Fig. 2; Tables 1, 2) and the overwhelming presence of multiserial to oligoserial radulae within the outgroup of non-aeolidaceans (represented in the present analysis by the families Tritoniidae and Janolidae, Figs 1, 2; Tables 1, 2). The family Notaeolidiidae has already been morphologically supported as an early diverged taxon within Aeolidacea (Wägele 1990, Wägele and Willan 2000), and possesses an ‘ intermediary’ oligoserial radula (with the number of longitudinal rows of the lateral teeth in total less than 10; Fig. 2; Tables 1, 2), thus less than the usual multiserial radula, but at the same time obviously more rows than a triserial radula (with only two longitudinal rows of the lateral teeth flanked by central teeth from each side), the triserial condition most likely preceded the uniserial radula in the evolution of Aeolidacea (see also character states justification in: Martynov et al. 2020). Next, the distribution of the triserial radulae among various aeolidacean superfamilies (Fig. 2) fits into a phyloperiodic pattern of evolution (Martynov and Korshunova 2022, present study; Tables 1, 2) because several superfamilies, including Flabellinopsoidea and Fionoidea, possess both triserial and uniserial families, and the new triserial superfamily Chudoidea superfam. nov., is related, although not precisely, to a node around both triserial Cumanotoidea and Flabellinoidea, along with uniserial Aeolidioidea, but not to other aeolidacean superfamilies (Figs 1, 2; see Synopsis of all Aeolidacean families throughout the text). However, the relative proportion of triserial and uniserial families within each superfamily varies greatly (Fig. 2; Tables 1, 2). For example, all Flabellinoidea are triserial, whereas within Flabellinopsoidea there is only one exception so far, the newly described uniserial flabellinopsoid family, Hantazuidae fam. nov. (see Synopsis below). In turn, almost all families of the superfamily Fionoidea (with the exception of the triserial family, Eubranchidae) are instead uniserial (Fig. 1, see Synopsis above). In the third largest aeolidacean superfamily recognized here, Aeolidioidea (after the exclusion of the previously incorrectly assigned members of the distantly related superfamily Flabellinoidea; see Synopsis below) include only a kernel of the closely related families such as Aeolidiidae, Myrrhinidae, Facelinidae, Favorinidae, Glaucidae, Babakinidae, and Pleurolidiidae (Figs 1, 2; Synopsis below) — the true aeolidioidean families — where triserial radulae are unknown. Considering that the three basal-most ‘ smaller’ aeolidacean superfamilies recognized here (see Synopsis above and below), corresponding to the three phylogenetically basal but morphologically highly disparate families, Apataidae, Samlidae, and Notaeolidiidae (sister to all other aeolidaceans; Figs 1, 2), are all either oligoserial or triserial, and that the triserial condition is present in all major aeolidacean superfamilies (Fig. 2), the triserial condition is likely the ancestral condition for all Aeolidacea, except Notaeolidiidae. The latter family is therefore last modern relic of the pre-triserial ancestral aeolidacean initial radiation. Whether the superfamily Chudoidea superfam. nov. will prove to have either a closer relationship to the superfamily Aeolidioidea (Fig. 2) or a somewhat more ‘ intermediate’ position toward the superfamilies Cumanotoidea, Flabellinopsoidea, and Flabellinoidea (Fig. 2), its discovery is a very important step for the comprehensive understanding of the evolution and systematics of the suborder Aeolidacea, because the pattern of the proportions of the triserial and uniserial families (Fig. 2; Tables 1, 2), and the high probability of the ancestral triserial state discussed above, clearly suggest that the triserial condition can relatively easily be reduced as an ontogenetic event over the course aeolidacean evolution, which, therefore, facilitates the formation of a uniserial radula multiple times in almost all major aeolidacean groups (Fig. 2; Tables 1, 2). A perfect example of such independent formation of a uniserial radula is the new family Hantazuidae fam. nov., which is uniserial but robustly placed as sister to the firmly triserial Flabellinopsidae, generally within the otherwise triserial superfamily Flabellinopsoidea (Fig. 2). The triserial superfamily Chudoidea superfam. nov. and Chudidae fam. nov. may, therefore, represent in turn some relic ‘ core’, ‘ mid-evolutionary’ aeolidacean radiation (that is partly reflected in their low support as sister to superfamilies Aeolidioidea, Cumanotoidea, Flabellinopsoidea, and Flabellinoidea; Figs 1, 2) preserved in the deep-sea environment, based on which the subsequent definite superfamilies, either predominantly triserial such as Flabellinoidea and Cumanotoidea, or predominantly uniserial, such as Aeolidioidea have been ‘ finally’ formed (Fig. 2). Chudo gen. nov. (Figs 1, 2, 6) urn: lsid: zoobank. org: act: E 845532 A-E 59 D- 48 C 7 - 8039 - 52 B 48109 DFAD Type species: Chudo humanistica gen. et sp. nov .. Diagnosis: Body considerably wide and massive. Notal edge completely reduced, dorsal part of the body smoothly transits to the lateral part. Ceratal rows distinct, separate, moderate in number, not stalked. Rhinophores smooth to wrinkled. Anus partly mixed — pleuroproctic in a higher cleioproctic position in an extreme body placement. No elaborate oral glands. Masticatory edges of jaws smooth. Radula formula 1.1.1. Triserial radula is remarkable with very massive lateral teeth. Central teeth square to triangular, with a strong non-compressed cusp. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. Single distal receptaculum seminis present. Vas deferens long, convoluted, prostate non-distinct. Massive external permanent penial collar absent. Definite penis not detected. Remarks: See above after the new family diagnosis.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF93FFF3FEF2FEEBFC15FDAE.taxon	description	(Fig. 6) urn: lsid: zoobank. org: act: 9 AB 97 F 43 - 2 FCA- 4624 - B 7 B 0 - BF 276 E 91 C 14 F	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF93FFF3FEF2FEEBFC15FDAE.taxon	etymology	Etymology: See above after the new family diagnosis.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF93FFF3FEF2FEEBFC15FDAE.taxon	materials_examined	Holotype: KM 883, L = 46 mm (preserved), Southern Ocean, subantarctic waters, R / V ‘ Akademik Mstislav Keldysh ’, cruise 79, sta. 6604, 61.1059 S 49.6952 W, 26 January 2020, depth 2800 m. Description External morphology (Fig. 6 A – C) Body very wide. Notal edge is completely reduced, dorsal part of the body smoothly transits to the sides. Rhinophores strong, smooth to slightly wrinkled, no less than two times longer than oral tentacles (in preserved state). Head is broad. Dorso-lateral parts of body bear very distinct, broadly elongated areas of the ceratal attachments, corresponding to the digestive gland branches, and appear as rather unbranched, but thick and ‘ compounded’ rows. In total up to about seven ceratal rows, from which four to five possibly represent the anterior digestive gland. Dorsal cerata almost completely fallen off during collection, only one or two relatively thin cerata are preserved. Anal opening mixed — pleuroproctic in a higher cleioproctic position, but placed in almost a posterior extreme of the right lateral side. Foot broad with anterior ‘ bilabiate’ furrow and evident anterior foot corners. Colour Live colour was unrecorded before fixation, in fixed state colour whitish to light brownish. Jaws (Fig. 6 D, E) Jaws massive, somewhat squarish in general outline, yellowish in colour. The masticatory edges smooth. Radula (Fig. 6 F – M) Triserial radula is remarkable with very massive lateral teeth, whose bases broader than bases of somewhat posteriorly square and more anteriorly triangular central teeth. Radula formula up to at least 37 × 1.1.1. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. No less than up to 30 denticles on the central teeth, and up to 35 denticles on inner edge of the lateral teeth. Cusp of central teeth strong, massive, triangular, to considerably pointed, some cusps not clearly delineated from lateral denticles. The denticles on the lateral teeth placed mostly on the inner edge, but outer edges may bear some serration or weak denticulation. Reproductive system (Fig. 6 O) Hermaphroditic duct leads to long, swollen, moderately wide convoluted ampulla. Vas deferens long, convoluted, prostate non-distinct, although prostatic region can be partly recognized. Supplementary gland absent. Oviduct connects through the insemination duct into the female gland complex. Vas deferens with no detectable penis within a penial sheath and oviduct opens in a common atrium open below approximately the 3 rd to 4 th ceratal rows. Receptaculum seminis relatively small, oval in a distal position, almost sessile, on a very short stalk. Ecology: Deep-sea taxon, discovered at a depth of 2800 m. Distribution: So far discovered only from the subantarctic location in the Southern Ocean. Remarks: The COI minimal uncorrected p - distance of 11.2 % was found between the Chudo humanistica gen. et sp. nov. and Microchlamylla amabilis. The COI maximal uncorrected p - distance of 23.6 % was found between the C. humanistica gen. et sp. nov. and Glaucilla marginata. See above after the new family diagnosis.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF91FFF1FF13FF05FDAEFC4C.taxon	description	(Figs 1, 2, 6; Tables 1 – 3) urn: lsid: zoobank. org: act: F 1 C 58 FA 3 - 1847 - 4 A 74 - 93 EC- 716 C 5 FDB 4 B 7 C Diagnosis: Aeolidacean superfamily with triserial radula. Body considerably wide and massive. Notal edge completely reduced, dorsal part of the body smoothly transits to the lateral part. Ceratal rows distinct, regular, separate, moderate in number, not stalked. Rhinophores smooth to wrinkled. Anus partly mixed — pleuroproctic in a higher cleioproctic position, remarkably, in an extreme posterior body placement. Anterior foot corners present. No elaborate oral glands. Masticatory edges of jaws smooth. Radula formula 1.1.1. Triserial radula is remarkable with very massive lateral teeth. Central teeth square to triangular, with a strong non-compressed cusp. Both central and lateral teeth bear numerous fold-like, partly clustered denticles. Single distal receptaculum seminis present. Clasping organ in female part of reproductive system absent. Vas deferens long, convoluted, prostate non-distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Definite penis not detected. Families included: Chudidae fam. nov .. Remarks: See under family Chudidae fam. nov ..	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF3FF93FE82FF72FBFCFDDF.taxon	description	(Figs 1, 2, 13; Table 5) urn: lsid: zoobank. org: act: C 3 AB 35 BB- 1 AEF- 456 A- 8868 - 69308 A 4 FCE 6 D Type species: Coryphella alexanderi Ekimova, 2022. Etymology: From the Latin corrupta meaning ‘ damaged’ in reference to the discontinuous, incomplete notal edge in this genus compared to the well-defined, continuous notal edge in the sister-genus Himatina, and that according to the original description (Ekimova 2022: 45) most of the type specimens were damaged during collection. Diagnosis: Body moderately narrow. Notal edge present, discontinuous. Cerata in several groups. Rhinophores smooth with fine wrinkles. Anterior foot corners present. Central teeth with non-compressed, narrow cusp, and distinct denticles. Lateral teeth denticulated with attenuated process basally. Only distal receptaculum seminis is illustrated, whereas in description both distal and proximal receptaculum seminis are mentioned. Vas deferens moderately long, distinct prostate, an oval penial sheath. Penis oval, partially broadened in the middle, tapering to a blunt conical end. Species included: Corrupta alexanderi (Ekimova, 2022) comb. nov .. Remarks: Four Corrupta alexanderi comb. nov. form a maximal supported clade, sister, but with low support (PP = 0.97, BS = 51), to the Himatina clade (Fig. 13). It should be noted that alignment of the 16 S gene of C. alexanderi comb. nov. specimens WS 14380, MIMB 42469 a, MIMB 42469 b, and MIMB 42468 revealed 27 additional nucleotides in the WS 14380 (MZ 821310) data (Supporting Information, Fig. S 2 A). Using all these data and simultaneously using GBlocks (which removed certain regions of the 16 S gene), critically impacted the validity of the results of the molecular phylogenetic analyses in Ekimova et al. (2022). In the present study, data from MZ 821310 and GBlocks were not used. Corrupta gen. nov. readily differs from Himatina (Korshunova et al. 2017 a) by the combination of a moderately narrow body with discontinuous notal edge, non-perfoliate rhinophores and by the considerably different details of the radular patterns including elongated-triangular central teeth of the radula, which are not nearly pectinate as in the genus Himatina. The new genus, therefore, significantly differs from the phylogenetically related Himatina, which well highlights the multilevel fine-scale diversity of external features, anatomy, and molecular phylogenetic data (Figs 1, 13). There are several inconsistencies between the description and figures in the original description of C. alexanderi (Ekimova 2022). Particularly, it is indicated on page 44 (op. cit.), that ‘ Cerata in continuous rows, not united in separated groups’; however, in figure 2 D (op. cit) distinct ceratal groups are clearly present. Furthermore, it is indicated on the same page that C. alexanderi has ‘ Distinct distal and proximal receptaculum seminis, both small muscular sacs’; however, in figure 4 (Ekimova 2022: 47) only a single distal receptaculum seminis is unequivocally depicted (see also details in the Results in the present study). Finally, the penis is described as (p. 44, op. cit.) ‘ broad, conical’, but the figure of the reproductive system (Ekimova 2022: fig. 4) clearly depicts that the penis is oval, only partially broadened in the middle, and at best tapered to a blunt conical ending, but surely not strictly ‘ conical’ (Supporting Information, Fig. S 2 B). Given these clear inconsistencies in the new genus we have included descriptions of the characters that correspond to the respective figures, not to the likely erroneously described characters in the text of Ekimova (2022). Comparison of the new genus Corrupta gen. nov. with all valid, currently included Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF9FF91FC49F9E9FB26FEC4.taxon	description	(Figs 1, 2, 13 – 16; Table 5) Korshunova et al. 2017 a: 28 – 29, Coryphella restricted. Type species: Eolidia verrucosa M. Sars, 1829. Diagnosis: Body moderately narrow. Notal edge almost completely reduced. Cerata in several groups. Rhinophores smooth with small tubercles. Anterior foot corners present. Central teeth with non-compressed moderately wide cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Distal and proximal receptaculum seminis. Moderately short vas deferens expands to a broad penial sheath, prostate distinct, S-shaped. Penis disk-shaped with numerous small triangular processes at the disk edge. Species included: Coryphella pseudoverrucosa Martynov et al., 2015, reinstated, Coryphella longicaudata O’Donoghue, 1922, reinstated, and Coryphella verrucosa (M. Sars, 1829), restricted in Korshunova et al. 2017 a and herein (Figs 13 – 16). See detailed details. P, jaw, SEM. Q, details of masticatory process of jaw, SEM. R, details of masticatory process of jaw, SEM. S, radular teeth, posterior part of radula, SEM. КM 565 (T – W), Rich Passage, Washington, USA, 12.5 mm length (live). T, dorso-lateral view. U, living animal on substrate. V, details of cerata. W, radular teeth, posterior part of radula, SEM. X, scheme of reproductive system. Scale bars: D, 100 μm; E, 50 μm; F, 50 μm; H, 100 μm; I, 30 μm; J, 10 μm; K, 30 μm; L, 10 μm; P, 200 μm; Q, 100 μm; R, 10 μm; S, 100 μm; W, 50 μm; X. 0.5 mm. Photos: Karin Fletcher (A – C, G, T – V), Tatiana Korshunova (M – O). SEM images: Alexander Martynov. Abbreviations: a, ampulla; an, anus; fgm, female gland mass; go, genital opening; p, penis; pr, prostate, psh, penial sheath; rsd, receptaculum seminis distal; rsp, receptaculum seminis proximal; vd, vas deferens. morphological data in Korshunova et al. (2017 a), and in the present study. Remarks: The genus Coryphella significantly differs from all genera of the family Coryphellidae by the combination of an almost completely reduced notal edge (the last remnants may be detected, after a very scrupulous study mostly below the anterior ceratal clusters, and thus there is no considerable ambiguity to consider that state also as ‘ completely reduced’), smooth to slightly tuberculate rhinophores, non-compressed cusp of central teeth, lateral teeth without an attenuated process basally, a disk-shaped penis with small triangular processes, and a distinct S-shaped prostate (previosly considered as a part of prostatic vas deferens). Importantly, this complex of characters is stable and morphologically recognizable in no less than three separate species of true Coryphella: C. longicaudata, C. pseudoverrucosa, and C. verrucosa (see detailed explanation and discussion below; Figs 13 – 16). Instead of a putatively single species’ distribution over both the North Atlantic and the North Pacific, at least three evidently separate species exist within the proper genus Coryphella, each with its own complex evolutionary history (Korshunova et al. 2017 a, present study; Figs 1, 2, 13 – 16). In the present study, three species within the Coryphella clade were revealed. C. pseudoverrucosa clustered in a distinct and separate clade (PP = 0.99, BS = 91), sister to the separate clade C. longicaudata (PP = 1, BS = 95), except for specimen WS 14404. Sister-clades C. pseudoverrucosa and C. longicaudata branch directly from the clade containing C. verrucosa (Fig. 13). The haplotype network based on the COI gene marker was calculated in the present study to evaluate the genetic distribution of the different haplotypes within the Coryphella complex. The results showed a network of haplotypes (Fig. 14 A), that clearly cluster into three groups coincident with Coryphella verrucosa (M. Sars, 1829), original description in Sars (1829), C. pseudoverrucosa Martynov et al., 2015, original description in Martynov et al. (2015), and a species classified here as C. longicaudata O’Donoghue, 1922 (original description in: O’Donoghue 1922 a), reinstated. To provide robust taxonomic assessment, neotype KM 569, 17 mm length (live), for C. longicaudata is selected here from Tacoma, Washington, USA, collected on 9 November 2014 by Karin Fletcher at the depth 13.4 m, from the geographic region close to the type locality, which included both the southern part of British Columbia (Canada) and San Juan Islands, Washigton, USA (O’Donoghue 1922 a). The external, jaws, and radular characters of the neotype are presented in Figure 15 A – F. Intragroup and intergroup genetic distances for the COI marker are shown in Table 6. Uncorrected COI p - distances within the Coryphella verrucosa group are 0 – 2.0 % and within the C. pseudoverrucosa group are 0 – 1.2 %. Uncorrected COI p - distances between C. verrucosa and C. pseudoverrucosa are 2 % – 3.7 %. The distances within the C. longicaudata group are 0 – 2.0 % and within the C. longicaudata dataset (except specimen WS 14404) are 0 – 1.7 %. The distances between C. longicaudata and C. pseudoverrucosa are 1.7 / 1.8 – 3.5 % (see details in Table 6). Thus, the distances between C. pseudoverrucosa and C. verrucosa, as well as between C. pseudoverrucosa and C. longicaudata, exceed the intraspecies’ genetic distances. The distances between C. longicaudata and C. verrucosa are 0.8 / 1.3 – 3.5 % (see details in Table 6), therefore, C. longicaudata is genetically closer to C. verrucosa than to C. pseudoverrucosa, despite the fact that C. verrucosa and C. longicaudata live in different oceans, while the distribution of C. longicaudata and C. pseudoverrucosa overlaps (Fig. 14 B). This case is similar to the recently discovered, very interesting phylogeographic and taxonomic patterns within the family Trinchesiidae from another superfamily (Fig. 2), where the NW Pacific Diaphoreolis zvezda Korshunova et al., 2023 is sister to the geographically highly remote North Atlantic Diaphoreolis stipata (Alder and Hancock, 1843) and more distantly related to the geographically closer NW Pacific species Diaphoreolis midori Martynov et al., 2015 (see: Korshunova et al. 2023). The distribution of C. verrucosa and C. pseudoverrucosa also shows distinct differences (Fig. 14 B). All 111 analysed C. verrucosa specimens were distributed in the North Atlantic and only touched the south-eastern border of the Arctic areas (at the Vaigatch island location on the East and at the Nunavut location on the West; Fig. 14 B). Whereas 21 analysed C. pseudoverrucosa specimens were collected from the north-west Pacific (Sea of Japan, Kurile Islands, and Kamchatka), but never in the north-east Pacific. Twenty-three specimens of the third haplogroup (C. longicaudata) were collected from both the north-west and north-east Pacific Ocean and their habitats in the north-west partially overlap with C. pseudoverrucosa (the Kurile Islands area and Kamchatka), Fig. 14 B. Thereby, the molecular-phylogenetic analyses, the haplotype network, and phylogeographical results clearly indicate three different haplogroups, related to three different species: C. verrucosa, C. pseudoverrucosa, and C. longicaudata (Figs 13, 14 A, B). Results published in Ekimova et al. (2022) also revealed three haplogroups, named Haplogroups A, B, and C. However, the genetic distances were calculated only between haplogroup A and haplogroup B + haplogroup C (Ekimova et al. 2022, table 1). Besides, the haplogroup names B and C were mistakenly mixed up in the text and in figure 3 A (see Supporting Information, Fig. S 1 A – C, in the present paper, all errors marked in red). The data for the specimen listed under number MIMB 14404, published in Ekimova et al. (2022), needs to be discussed separately here. This specimen according to our analysis belongs to C. longicaudata. In Ekimova et al. (2022), the specimen MIMB 14404 belongs to haplogroup A in the text of the paper, but haplogroup B in figure 6, which according to fig. 3 A is haplogroup C (Supporting Information, Fig. S 1 D). Thus, the minimum interspecific uncorrected p - distances in Ekimova et al. (2022) calculated between C. verrucosa specimens erroneously included data for specimen MIMB 14404 and combined specimens from haplogroup B and haplogroup C (C. pseudoverrucosa and C. longicaudata). Which is why in Ekimova et al. (2022) the distances within ‘ C. verrucosa ’ is 2.3 %, within ‘ C. pseudoverrucosa ’ it is 3.2 %, and between ‘ C. verrucosa ’, and ‘ C. pseudoverrucosa ’ is 0.9 % (Fig. S 1 C). We analysed the COI data for specimen MIMB 14404 and concluded that these more variable data may be the result of a technical sequencing error or may appear for some other reason, but this specimen is closer to the C. longicaudata group. We also calculated the genetic distances excluding the molecular data of MIMB 14404 and found that these data do not significantly affect the results. Nevertheless, these data could have had a bearing on the credibility of the species’ delimitation results in Ekimova et al. (2022). Thus the species that are molecularly closer to each other, C. verrucosa and C. longicaudata, inhabit geographically distant regions of the Atlantic / south-east sub-Arctic and Pacific Oceans. Coryphella pseudoverrucosa and C. longicaudata show distinct differences according to their genetic distances, despite overlapping ranges. Three distinct haplogroups in the Coryphella verrucosa complex were discussed in Ekimova et al. (2022), but the genetic distances were analysed only between two groups, with mixed data for C. longicaudata, which led to the erroneous conclusion that C. verrucosa and C. pseudoverrucosa are the same species. In addition, a map showing the distribution of the Coryphella verrucosa complex is absent from that work and the names of the locations are misleading. The localities for C. verrucosa noted as Norway and NW Atlantic are attributed to the Atlantic Ocean and those noted for the White Sea, Barents Sea, Kara Sea, and ‘ Canadian Arctic’ are attributed to the Arctic Ocean. In reality, all the ‘ Arctic’ waters are not the true arctic waters but are close to boreal, temperate regions. The Barents Sea is in reality the continuation of the boreal, temperate waters of Norway. The Kara Sea (mentioned due to Vaigatch Island) is only the border between the Kara and Barents Seas, and thus still under the influence of the Barents Sea, not the actual Arctic Seas. The localities in the waters of Canadian Nunavut and Labrador are also close to boreal regions. When species are mentioned as ‘ trans-Arctic’ it suggests that species should habitat the true cold Arctic seas, such as the Laptev, East Siberian, and Chukchi Seas. The distribution of C. longicaudata in Alaska is so far limited to Fishermen’s Bend, Juneau, which is also close to boreal temperatures and does not apply to all Alaskan waters, and surely does not include true Alaskan Arctic waters. It was previously concluded (Martynov et al. 2015: 61) that ‘ In the Arctic C. verrucosa is credibly absent (Martynov 2006 b), and is not distributed to the East, far than the Barents Sea, which practically excludes gene exchanges between C. verrucosa and Pacific C. pseudoverrucosa. ’ Since that time there are no data to disprove that conclusion. Therefore, describing the habitat of C. verrucosa as ‘ Arctic’ in Ekimova et al. (2022) is not the real Arctic. The distribution map of C. verrucosa, C. pseudoverrucosa, and C. longicaudata (mixed together under the single name C. verrucosa) is provided in Ekimova et al. (2024), fig. 2 l. However, this figure is misleading: distributions of these species are presented to be more ‘ Arctic’ than they really are and some habitats are incorrectly marked in red. Fishermen’s Bend (Alaska) is not very far from definitely non-Arctic British Columbia, but both the Bering Sea and Bering Strait are marked in red. Vaigatch Island is located between the Kara and Barents Seas, but the entire Kara Sea is also marked in red. Franz Josef Land is incorrectly marked in red. The localities Disko Island (Greenland) and Durban Harbour (Nunavut) are both marked as Canadian Arctic. Although Nichols (1900) and Lemche (1929) listed ‘ Coryphella rufibranchialis ’ from the Bering Sea, these were lists without any detailed analysis of any particular material and as such may represent other genera of Coryphellidae or completely unrelated Aeolidacea, and cannot be relied upon, therefore, with any credibility, and cannot be used for any phylogeographic analysis. In a later book based on Lemche’s observations (Just and Edmunds 1985) there is no mention of the Bering Sea for Coryphella verrucosa. Using only morphological data, we previously concluded that the North Pacific true Coryphella, including the more southern parts of the Bering Sea, may represent separate species, which at the level of lists would have been presented as Coryphella ‘ verrucosa ’ (Martynov 2006 b) at that time. Therefore, it is completely unsubstantiated to consider the distribution of Coryphella ‘ verrucosa / rufibranchialis ’ to be ‘ pan-Arctic’ using species’ lists from well before the molecular era. Morphological descriptions in Ekimova et al. (2022) for C. verrucosa also contain much inaccurate data. One example is the radulae of C. verrucosa, which are given in figure 6 A – H [here and in the remainder of this paragraph figures refer to figures in Ekimova et al. (2022)]. Particularly, for the specimens whose radulae are illustrated in fig. 6 A, B there are no molecular data. Therefore, the radula of C. verrucosa is reliably presented only in fig. 6 C. Further, fig. 6 D – H is a mixture of C. pseudoverrucosa and C. longicaudata (for details see Supporting Information, Fig. S 1 D). In the present study, a Phyloperiodic Table was built (Fig. 16, present study) for the comparison of radular patterns of C. verrucosa, C. pseudoverrucosa, and C. longicaudata. On the basis of the molecular phylogenetic tree for three species of the genus Coryphella (= three groups), periods were built for each of the groups, depending on the dimension between the central cusp of the central teeth of the radula and the border of the lateral denticles (marked in yellow on Fig. 16, present study). In total four periods (<30 μm, 30 – 50 μm, 50 – 100 μm,> 100 μm) were built. All available data for each of the three groups were given at the same scale and arranged into these four periods. Data from Ekimova et al. (2022: fig. 6 С – H) were accurately redrawn with the original scale and placed into the periods in relation to the dimension between cusp and lateral denticles (Fig. 16, present study). After filling in the Table, it was revealed that all radulae (fig. 6 С – H), which have been presented as comparative material in Ekimova et al. (2022), belong to juvenile and subadult specimens and belong in I and II periods. It is well known that in juveniles of different molluscan taxa, morphological differences are significantly weaker compared to adults (Martynov and Korshunova 2015). For illustration of the morphological characters of the radula in Ekimova et al. (2022), the radulae of adult specimens were not given; however, having a huge sequencebased dataset doubtless includes adult specimens. Using only juvenile or subadult radulae produced an incorrect impression about the putative absence of morphological differences in ‘ C. verrucosa ’ and, therefore, led to false conclusions about the true number of species Ekimova et al. (2022). Applying the Phyloperiodic Table, the following morphological patterns have been revealed: adult C. verrucosa possess a shorter cusp of the central teeth with longer lateral teeth, adult C. pseudoverrucosa possess a longer, massive cusp with shorter lateral teeth, and adult C. longicaudata possess a longer and wider cusp with longer lateral teeth (Fig. 16, present study). More fine-scale differences along this spectrum are expected, but general trends in the adult radular patterns within these three species are evident. These fine-scale characters further support a multilevel organismal diversity system where application of both morphological and molecular data has recently been employed on a practical basis in other groups of nudibranchs (Korshunova and Martynov 2024). The genus Coryphella forms a distinct clade according to the molecular phylogenetic analysis (Figs 1, 13). Merging all the taxa of the family Coryphellidae into a single genus ‘ Coryphella ’ would completely dismiss the extensive, considerable morphological diversity of the large-scale to the fine-scale differences (Korshunova et al. 2017 a, present study) within Coryphellidae, disregard the obvious extensive molecular phylogenetic diversity (Figs 13, 14), and destroy taxonomy, per se, since all the significant and indisputable differences of the entire Coryphellidae family (see below for a detailed synopsis) would need to be presented under the single pan-lumping name ‘ Coryphella ’. Such an action would represent nothing more than the formation of a completely non-diagnosable pseudo-unit with a collection of almost all possible character states, overlapping not only between more related families such Paracoryphellidae and Flabellinidae, but also between very distantly related families such as Samlidae and Facelinidae (see Synopsis above and below of all Aeolidacean families, Tables 1 – 4, and molecular phylogenetic tree in Figs 1, 2). Furthermore, there is even finer-scale epigenetic diversity within the proper genus Coryphella, since a taxon / species C. rufibranchialis apparently does not show significant genetic differences from C. verrucosa (Eriksson et al. 2006), but readily differs from it morphologically by the presence of markedly longer cerata, to such degree that it may be treated as a separate species (Picton and Morrow 2023, 2024). All these large-scale and fine-scale differences are undoubtedly the results of the evolutionary process at different levels, but they are all clearly ignored when taxonomically the name ‘ Coryphella ’ is incorrectly applied to cover all the significant morphological and molecular diversity of the family Coryphellidae (Fig. 13). Comparison of the genus Coryphella with all the valid, currently included Coryphellidae genera is presented in Table 5. See also detailed considerations in Results and Discussion (Figs 1, 2, 13).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF87FF99FEEAF8D6FE5FFD7A.taxon	description	(Figs 1, 2, 13; Table 4)	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF87FF99FEEAF8D6FE5FFD7A.taxon	description	Korshunova et al. 2017 a, the family Coryphellidae reinstated: 25 – 7. Diagnosis: Body wide to narrow. Notal edge reduced, more commonly discontinuous to almost completely reduced, but may also be continuous in several genera. Cerata not stalked, in numerous continuous or discontinuous rows. Rhinophores smooth, wrinkled, rarely annulate or perfoliate. Anus pleuroproctic under a reduced notal edge. Elaborate oral glands commonly absent. Masticatory edges of jaws bear several rows of compound, sharpened or tubercle-like denticles. Radula formula 1.1.1. Central teeth usually with distinct, non-compressed (= undepressed) cusp, more rarely compressed by adjacent lateral denticles to various degrees. Lateral teeth narrow or with attenuated process basally, usually denticulated. Commonly both distal and proximal receptaculum seminis present. Vas deferens usually short, rarely long, with relatively distinct or indistinct prostate. Accessory gland distinct only in the single genus Occidenthella. Massive external permanent penial collar absent. Penis internal, in many cases broad to disk-shaped, more rarely elongated conical, unarmed. Genera included: Borealea Korshunova et al., 2017, reinstated, Coryphella Gray, 1850, restricted, Fjordia Korshunova et al., 2017, reinstated, Gulenia Korshunova et al., 2017, reinstated, Himatina Thiele 1931, reinstated, Itaxia Korshunova et al., 2017, reinstated, Microchlamylla Korshunova et al., 2017, reinstated, Occidenthella Korshunova et al., 2017, reinstated, Orienthella Korshunova et al., 2017, reinstated, Corrupta gen. nov., and Portorchardia gen. nov. Remarks: See Results and Discussion and also Remarks in Synopsis of coryphellid genera below. Both analyses in Korshunova et al. (2017 a), and the present study, (Figs 1, 2, 13) reveal a similar topology to the genera Fjordia, Gulenia, Himatina, Coryphella, Borealea, Occidenthella, Orienthella, Microchlamylla, and Itaxia, regardless of the number of analysed specimens and outgroup taxa. Two new genera, Corrupta gen. nov. and Portorchardia gen. nov., were revealed in the present study. Besides this, adding molecular data belonging to the genus Fjordia for Fjordia capensis, and to the genus Orienthella for Orienthella cooperi and Orienthella fogata, which were correctly predicted in Korshunova et al. (2017 a) by morphological characteristics (according to the original descriptions), did not affect the tree topology. Genera clustered in distinct and separate clades Fjordia (PP = 1, BS = 98), Gulenia (PP = 1, BS = 98), Himatina (PP = 1, BS = 100), Corrupta gen. nov. (PP = 1, BS = 100), Portorchardia gen. nov. (PP = 1, BS = 100), Coryphella (PP = 1, BS = 100), Borealea (PP = 0.95, BS = 58), Occidenthella (PP = 1, BS = 100), Orienthella (PP = 1, BS = 93), Microchlamylla (PP = 1, BS = 100), and Itaxia (PP = 1, BS = 91) within the family Coryphellidae (Fig. 13). A comparison of all valid, currently included Coryphellidae genera is presented in Table 5. For genera of the family Coryphellidae we provide detailed diagnoses in order to reinstate them. As we also argued in detail under Remarks to the family Facelinidae (which contains a large number of truly fine-scale genera with morphological differences that are often minor and difficult to properly recognize) if all the genus-level diversity within the family Coryphellidae were lumped together, then inevitably a major part of Facelinidae genus-level diversity (and ultimately, the diversity within all other Aeolidacea families as well, see Discussion) must be synonymized with the oldest facelinid genus Phidiana Gray, 1850 because precisely the same logic of seeming ‘ intermediate’ morphology was applied when the genus-level diversity of the family Coryphellidae — with its fine-scale diagnostics comparable to the fine-scale diagnostics of the genera of the family Facelinidae — was lumped into the putatively ‘ same’ genus ‘ Coryphella ’ (Ekimova et al. 2022). Therefore, as a consistent part of general fine-scale taxonomy, thoroughly employed in the present study from the order Nudibranchia downstream to family and genera levels (see Synopsis of all the families of the suborder Aeolidacea above and below), an updated detailed synopsis with respective diagnoses of the recently described genera and two new genera of the family Coryphellidae are provided below (Figs 1, 2, 13; Table 5).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9EFFFEFF1DFA16FB03FCCF.taxon	description	(Figs 1, 2; Table 4) Odhner 1907: 26. Korshunova et al. 2017 a: 67, 72, 73, supplementary materials. Martynov et al. 2020: 1, 3, 12 – 15. Diagnosis: Body moderate. Notal edge completely reduced. Ceratal rows regular, numerous cerata on elevations per row. Rhinophores smooth. Anus acleioproctic in anterior / middle part of body. Masticatory edges of jaws bear a single to several rows of denticles, rarely smooth. Radula formula 1.1.1. Central teeth with cusp not compressed by adjacent lateral denticles. Lateral teeth narrow or with moderately attenuated process basally, usually denticulated, rarely smooth. Commonly two proximal receptaculum seminis. Special clasping organ in female part of reproductive system with small hooks may present. Vas deferens moderate in length, prostate moderately distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, narrow, rolled, armed or unarmed. Genera included: Cumanotus Odhner, 1907. Remarks: The family Cumanotidae shows a highly peculiar combination of complete reduction of the notal edge, regular ceratal rows, acleioproctic anus in the anterior to middle parts of the dorsal side with a triserial radula, and a special clasping organ, not in the male, but in the female reproductive system in several representatives. No one superfamily and family of the suborder Aeolidacea can approach that very special combination found within the family Cumanotidae. The reduction of the notal edge and acquisition of the regular ceratal rows proceeded in the family Cumanotidae, and in the superfamily Cumanotoidea, independently from other superfamilies (Figs 1, 2; Table 3, Table 4). The family Cumanotidae also has a highly unusual ‘ double’ life mode, which combines both burrowing behaviour with partial swimming, and includes a body shape with a peculiar arrangement of cerata that mimics the large tubulariid hydroids on which it feeds, which in total contributes to a bizarre combination of morphology and molecular patterns.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9FFFFEFCDDF974FE46FAE2.taxon	description	(Fig. 2; Tables 1 – 3) Diagnosis: Aeolidacean superfamily with triserial radula. Body moderate to very narrow. Notal edge completely reduced. Ceratal rows regular or strongly reduced in paedomorphic representatives. Numerous cerata on elevations per row, or reduced. Rhinophores smooth or completely reduced along with oral tentacles in paedomorphic representatives. Anus acleioproctic in anterior / middle part of body. Anterior foot corners present or absent. Commonly no elaborate oral glands. Masticatory edges of jaws bear single to several rows of denticles, rarely smooth. Central teeth with non-compressed cusp. Lateral teeth usually denticulated, rarely smooth. Proximal receptaculum seminis. Clasping organ in female part of reproductive system with rosettes of hooks may be present. Vas deferens moderately long to short, prostate indistinct or distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, narrow, armed or unarmed. Families included: Cumanotidae Odhner, 1907 and Pseudovermidae Thiele, 1931. Remarks: Although the superfamily Cumanotoidea possesses a triserial radula and historically has been associated with Flabellinoidea, according to recent (Martynov et al. 2020) and the present analyses (Figs 1, 2), Cumanotoidea do not show a direct relationship to Flabellinoidea. An immediate difference of all Cumanotoidea from a majority of Flabellinoidea is the absence of a distinct notal edge, few regular, not significantly branched, ceratal rows, and the presence of a special clasping organ in the female part of the reproductive system. The present molecular phylogenetic analysis clearly indicates that there is not high support for Cumanotoidea, even if they were basal to Flabellinopsoidea and Flabellinoidea (Fig. 1), but are more commonly placed as sister to both major superfamilies Aeolidioidea and Flabellinoidea (Martynov et al. 2020), or to four superfamilies: Chudoidea superfam. nov., Aeolidioidea, Flabellinopsoidea, and Flabellinidae (present study Figs 1, 2). Also, considering the morphological disparity between Flabellinoidea and Cumanotoidea, separate superfamily status is highly justified for the latter. The sister-status of the profoundly paedomorphic, worm-shaped family, Pseudovermidae, to Cumanotidae has been shown in several separate molecular phylogenetic analyses (Martynov et al. 2020, present study; Figs 1, 2), and the family Pseudovermidae is, therefore, included in the superfamily Cumanotoidea.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA6FFF9FC5DF913FAE8F83D.taxon	description	(Figs 1, 2; Table 4)	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA6FFF9FC5DF913FAE8F83D.taxon	diagnosis	Diagnosis: Body wide to narrow. Notal edge completely reduced. Cerata non-elevated, numerous per row. Ceratal rows branched or simple. Rhinophores smooth to wrinkled. Anus acleioproctic, more rarely cleioproctic. Masticatory edges of jaws bear several to single row of distinct, sharpened to compound denticles. Radula formula 0.1.0. Central teeth usually with strong to moderately distinct cusp, not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens usually moderate, prostate indistinct. Supplementary gland present, inserts into vas deferens in all confirmed cases. Massive external permanent penial collar absent. Penis internal, commonly narrow, unarmed, in one unique case very broad with a ring of lobes at the tip. Genera included: Cuthonella Bergh, 1884, type species, C. abyssicola Bergh, 1884, diagnosis is ‘ body wide with branched pre-anal ceratal rows, with up to at least 17 branched rows in the type species (minimum no less than c. seven to eight in included species), cleioproctic anus, protruding cusp of central teeth of radula with strong cusp not clearly delineated from lateral denticles in type species, to more distinct cusp, supplementary gland inserts to vas deferens on a considerable distance, penial sheath and penis non-widened, receptaculum seminis commonly distinct, on a very long, or a long stalk’, species and subspecies included C. abyssicola abyssicola Bergh, 1884, C. abyssicola kryos Korshunova et al., 2020, C. punicea (Millen, 1986), C. sandrae Korshunova et al., 2020. Fiocuthona Martynov, 1992, and type species F. concinna (Alder and Hancock, 1843), diagnosis is ‘ body narrow, up to six unbranched pre-anal rows, anus acleioproctic, radular teeth with commonly protruding, distinct cusp, penis with narrow base and supplementary gland insert to vas deferens relatively closer to penial sheath, commonly nonstalked, indistinct from very short stalk receptaculum seminis’, subspecies include F. concinna concinna (Alder and Hancock, 1843), F. concinna bellatula (Korshunova et al., 2020). Margina Martynov and Korshunova, 2025, and type species Margina cocoachroma (Williams and Gosliner, 1979), diagnosis is ‘ body narrow, up to four unbranched pre-anal rows, anus acleioproctic, radular teeth with commonly moderate to non-protruding cusp, penial sheath and penis with broadened base and supplementary gland inserted to the penis, the latter feature is unique for the family Cuthonellidae, but not confirmed independently, receptaculum seminis distinct with short stalk’. Nella Martynov and Korshunova, 2025, type species N. soboli (Martynov, 1992), diagnosis is ‘ body moderately wide to narrow, usually less than eight pre-anal ceratal rows, ceratal rows commonly unbranched to rarely partly branched, anus commonly acleioproctic (rarely cleioproctic), central teeth with distinct cusp and denticles, supplementary gland inserts into vas deferens commonly on a moderate distance, penial sheath not widened significantly, penis commonly elongated conical, without circle of lobes at the tip, receptaculum seminis distinct with a moderate stalk’; besides from type species, includes N. ainu (Korshunova et al., 2020), N. anastasia (Ekimova et al., 2024), N. benedykti (Korshunova et al., 2020), N. denbei (Korshunova et al., 2020), N. georgstelleri (Korshunova et al., 2020), N. hiemalis (Roginskaya, 1987), N. orientosiberica (Korshunova et al., 2020) comb. nov., N. osyoro (Baba, 1940), N. rgo (Korshunova and Martynov, 2022), N. yermolyevae Martynov and Korshunova, 2025. Penistella Martynov and Korshunova, 2025, and type species P. elenae (Martynov, 2000), diagnosis is ‘ body wide, ceratal rows mostly unbranched, but branched rows also present, more than 15 pre-anal rows, cleioproctic anus, radular teeth with protruding cusp and distinct denticles, supplementary gland inserts to vas deferens, but placed on penial sheath, penial sheath and penis very wide, tip of penis with star-like ring of papillae, receptaculum seminis distinct with a long stalk’. Developmentally, the genus Nella, including the type species N. soboli and at least several closely related species (Martynov 1992 a, Korshunova et al. 2021), exhibits direct development, whereas all so far known species of the genera Fiocuthona and Margina, and at least one species of the genus Cuthonella proper, undergo planctonic development (Millen 1986, Goddard 1991, Martynov and Korshunova 2011). These differences are consistent with the phylogeographic patterns, since Nella inhabits coldest true Arctic and NW Pacific shallow waters, whereas Fiocuthona inhabits boreal, temperate waters of the North Atlantic and NE Pacific, and Margina the single cuthonellid genus known so far, which definitely penetrates subtropical waters (Korshunova et al. 2021, Martynov and Korshunova 2025). Victima Martynov and Korshunova, 2025, type species V. vasentsovichi (Korshunova et al., 2020), diagnosis is ‘ body wide, ceratal rows branched, 10 and more branched and unbranched pre-anal ceratal rows, anus cleioproctic, central teeth with strong cusp and distinct denticles, supplementary gland inserts into vas deferens on a moderate distance, penial sheath not widened, penis elongated conical, unarmed, without circle of lobes at the tip, receptaculum seminis distinct with a moderate stalk’. Remarks: The family Cuthonellidae is the only family within Fionoidea with a number of species in which a supplementary gland is inserted into the vas deferens and not into penis (Martynov 1992 a, Korshunova et al. 2021). As mentioned above, such a character within Fionoidea is so far only reliably documented in a single restricted genus, Eubranchus, of the family Eubranchidae, which is distantly related to Cuthonellidae, and in the phylogenetically related, but otherwise dramatically different, family Calmidae, which itself contains only a few species (see below). Thus, we propose that insertion of a supplementary gland into the vas deferens is an ancestral feature, and potentially may be discovered within other taxa, which by no means can be considered as a basis for a family-level synonymyzation, because in every family there is a particular combination of characters of different levels. For instance, the family Cuthonellidae, represents a coherent, well-defined morphological and molecular (Figs 1, 2) taxonomic unit, combining in various genera, branched-to-simple ceratal rows, cleioproctic or acleioproctic anus, radula with protruding cusp, unarmed penis, and predominant presence of a supplementary gland inserted into the vas deferens (see genera Cuthonellidae synopsis above, and molecular phylogenetic analysis in: Korshunova et al. 2021). Therefore, if the family Cuthonellidae were lumped into putative ‘ Fionidae’, it would fundamentally obscure the unique combination of the ancestral insertion of a supplementary gland into the vas deferens plus various degrees of simplification of the initial branched ceratal pattern, thus fundamentally undermining any possibility for reliable diagnostics within any family of the superfamily Fionoidea and the suborder Aeolidacea because the true family Fionidae, with the inclusion of the stem-name bearing genus Fiona, does not possess any supplementary gland at all (see: Korshunova et al. 2017 c, 2021, 2022, Martynov and Korshunova 2025, present study, Synopsis above and below).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF98FFFBFEE7F917FEC5FC56.taxon	description	(Figs 1, 2; Table 4) Odhner 1934: 278.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF98FFFBFEE7F917FEC5FC56.taxon	diagnosis	Diagnosis: Body wide. Notal edge completely reduced. Ceratal rows branched to simple, numerous non-elevated cerata per row. Rhinophores smooth. Anus acleioproctic or cleioproctic. Masticatory edges of jaws commonly bear single row of compound, sharpened denticles. Radula formula 0.1.0. Central teeth with strong cusp not compressed by adjacent lateral denticles. Proximal and distal receptaculum seminis. Vas deferens moderately short, prostate indistinct. Supplementary gland present, inserts into penis. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Cuthona Alder and Hancock, 1855 [restricted only to three valid species, type C. nana (Alder and Hancock, 1842), C. divae Er. Marcus, 1961, and C. hermitophila Martynov et al., 2015] and Bohuslania, Korshunova et al., 2018. Remarks: About 45 years ago, almost all Fionoidean diversity (at that time listed under the family named Tergipedidae) was dismissively lumped into the seemingly single genus Cuthona [see an illustrated history of lumping events within the superfamily Fionoidea in Korshunova et al. (2021)] and that evolutionary and morphologically unsubstantiated action has lasted a considerable time, despite explicitly presented evidence of significant morphological and taxonomic heterogeneity within the so-called ‘ Cuthona’ for a long time (Martynov 1992 a, 2006 a, Martynov and Korshunova 2011). That lumping generated taxonomic confusion because under the putatively ‘ same’ genus-level such evidently different family-level taxa, such as Cuthonidae and Trinchesiidae, were concealed. However, when molecular phylogenetic data came into use, it became so obvious (although it had previously repeatedly been predicted) that ‘ Cuthona’ in no way could encompasses the uncovered molecular phylogenetic diversity (Fig. 2) corresponding to many families, and not merely a single genus ‘ Cuthona’ (Korshunova et al. 2017 c, 2018, 2021, 2022). It is also worth noting that an absolute majority of the fine-scale differentiated Fionoidea families — including Eubranchidae, Tergipedidae, Calmidae, Cuthonellidae, and Cuthonidae, which are well supported by molecular phylogenetic data — were proposed a long time ago (e. g. Bergh 1889, Iredale and O’Donoghue 1923, Odhner 1934, Miller 1971, 1977). The family Cuthonidae is fundamentally restricted to only the genus Cuthona proper, with the inclusion of several valid, fine-scale diagnosed species only from the North Atlantic and North Pacific. Species such as Cuthona nana (Alder and Hancock, 1842), Cuthona divae Er. Marcus, 1961 and Cuthona hermitophila Martynov et al., 2015, and not hundreds of highly heterogenous species from all over the world, which in reality belong to at least seven separate families (Figs 1, 2). Any other species of ‘ Cuthona’ that currently may be listed under this genus in WoRMS (2024) do not belong to Cuthona proper, and many of them belong to the family Trinchesiidae (see below). The true genus Cuthona, with only three currently recognized species, possesses a very characteristic semi-lunar head with oral tentacles placed toward the middle part of head, has branched ceratal rows, a commonly cleioproctic anal position, an unarmed penis and a supplementary gland inserted into the penis, and whose distribution is restricted to the temperate and cold waters of the Northern Hemisphere. So far, the only other confirmed genus within the family Cuthonidae, the genus Bohuslania Korshunova et al., 2018, is evidently a paedomorphic taxon with a reduced head and ceratal row structure, which inhabits a predominantly brackish environment in a fjord at the Swedish and Norwegian border (Korshunova et al. 2018). The lesson that needs to be learned both from the superfamily Fionoidea case in general, and the family Cuthonidae in this strongly-restricted sense in particular, is that the more differentiated the taxonomy of a group is, the more it reflects actual and always very complex evolutionary (phylogenetic) pathways. Even at the level of pre-molecular work, some of the current families and genera are partly poly- or paraphyletic. This is no reason to blame morphology-based taxonomy for previous attempts to make taxonomy as finely differentiated as possible, especially when some morphology-based studies predicted today’s fine-scale differentiation, which has been polished and improved by molecular phylogenetic methods (Synopsis; Figs 1, 2). In this respect, if further Fionoidea diversity is uncovered, especially in the deep sea, that potential diversity does not precisely ‘ fit’ into currently recognized families of the superfamily Fionoidea — either morphologically or molecularly, or both — this must not imply that family borders should be stretched or that morphological and molecular phylogenetic diversity (Figs 1, 2) should be lumped into an unmanageable, highly heterogenous putative ‘ family Fionidae’ or genus ‘ Cuthona’ sensu latissimo. Instead, more genus and family levels should be further separated following the incredibly complex at every possible level and ‘ endlessly beautiful’ (see: Darwin 1859, Carrol 2005) organismal evolutionary way.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFE8FF88FC79FDB5FAF9F894.taxon	diagnosis	Diagnosis: Body very narrow. Notal edge completely reduced. Cerata placed in single row on each side of body. Apical parts of cerata bear single or several cushion-like elevations, and may bear cnidosac-like structures. Oral tentacles absent, oral veil present instead. Rhinophores smooth. Anus pleuroproctic toward acleioproctic. Anterior foot corners absent. Elaborate oral gland present. Masticatory edges of jaws bear a single row of distinct denticles. Radula formula 0.1.0. Central teeth with relatively distinct non-compressed cusp. Distal seminal receptaculum. Vas deferens moderately long, may form distinct prostate adjacent to penis. Massive external permanent penial collar absent. Special supplementary gland or accessory in male part of reproductive system is absent. Penis internal, small, subconical. Genera included: Embletonia Alder and Hancock, 1851. Remarks: The superfamily Embletonioidea, reinstated with the single family Embletoniidae, represents distinctly paedomorphic taxa, comparable to evidently paedomorphic Tenellia proper in the family Trinchesiidae of the superfamily Fionoidea (Korshunova et al. 2022) according to its general body pattern, highly reduced number of cerata and presence of small oral veil instead of developed oral tentacles, and parallel to the independent formation of the partly externally similar, but otherwise completely different family Pseudovermidae (Martynov et al. 2020) from the genuine Aeolidacean superfamily Cumanotoidea (see Synopsis of all Aeolidacean families above; Tables 3, 4). According to the molecular phylogenetic analysis in Martynov et al. (2020) Embletoniidae appear as sister to the family Unidentiidae, whereas according to the phylogeny in Karmeinski et al. (2021) Embletoniidae show a rather unsettled position either basally to all Aeolidacea or within different (though related to Aeolidacea) non-aeolidacean suborder Janolacea. At the same time, previous considerations that Embletoniidae belong to the suborder Dendronotacea, can now be safely excluded. The family Embletoniidae, therefore, is not included in Tables 3 and 4 with a summary of diagnostic characters within aeolidacean superfamilies and families, but included here as an addition to the suborder Aeolidacea.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFE8FF88FF63F8A1FADCFD81.taxon	diagnosis	Diagnosis: Superfamily with uniserial radula. Notal edge completely reduced. Cerata placed in single row on each side of body. Apical parts of cerata bear single or several cushion-like elevations, and may bear cnidosac-like structures. Oral tentacles absent, oral veil present instead. Rhinophores smooth. Anus pleuroproctic toward acleioproctic. Anterior foot corners absent. Elaborate oral gland present. Masticatory edges of jaws bear a single row of distinct denticles. Central teeth with relatively distinct non-compressed cusp. Distal seminal receptaculum. Clasping organ in female part of reproductive system absent. Vas deferens moderately long, may form distinct prostate adjacent to penis. Massive external permanent penial collar absent. Special supplementary gland or accessory in male part of reproductive system is absent. Copulative apparatus small, simple, subconical. Families included: Embletoniidae Pruvot-Fol, 1954.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA2FFC7FC55F93DFBACF884.taxon	description	(Figs 1, 2; Table 4) Odhner 1934: 282. Martynov 1998: 763 – 77. Korshunova et al. 2017 c, family Eubranchidae validity confirmed: 9, 14, 17, 18. Korshunova et al. 2020 b: 21 – 3, 39. Diagnosis: Body wide to narrow. Notal edge completely reduced. Cerata non-elevated, numerous-to-few per row. Ceratal rows branched or simple. Rhinophores commonly smooth, rarely annulate or papillate. Anus acleioproctic, very rarely cleioproctic. Masticatory edges of jaws commonly bear single row of distinct denticles, commonly partly sharpened to compound. Radula formula 1.1.1, which is unique among members of the superfamily Fionoidea. Central teeth usually with small cusp, rarely massive, compressed or not compressed by adjacent lateral denticles. Lateral teeth thin, characteristically broadened laterally, commonly smooth, with or without strongly reduced denticles. Distal receptaculum seminis, or it is reduced in several taxa, absence of receptaculum is correlated with presence of a broad lobe-shaped penis, or with a special system of copulative stylets. Vas deferens usually short to moderate, prostate indistinct to distinct. Supplementary gland present; inserts into penis in absolute majority of taxa or, very rarely, in vas deferens. Massive external permanent penial collar absent. Penis internal, commonly armed, rarely unarmed. Three main patterns of copulative architecture: usual not considerably widened, commonly conical penis with a hollow stylet, or a broad lobe with numerous small spines, or a special system of macro- and microstylets in several genera, in which case penis is usually reduced. Genera included: Aenigmastyletus Martynov, 1998, reinstated, Amphorina Quatrefages, 1844, validity confirmed in Korshunova et al. (2020 b) and herein, Annulorhina Rao, 1968, reinstated, Capellinia Trinchese, 1873, validity confirmed herein, Corruptobranchus Martynov and Korshunova, 2025, Dunga Eliot, 1902, reinstated, Eubranchopsis Baba, 1949, reinstated, Eubranchulus Martynov and Korshunova, 2025, Eubranchus Forbes, 1838, restricted only to type species E. tricolor in Martynov (1998), Korshunova et al. (2020 b), and herein, Galvinella Eliot, 1907, reinstated, Karavellia Martynov and Korshunova, 2025, Leostyletus Martynov, 1998, validity confirmed herein, Longibranchus Martynov and Korshunova, 2025, Nihonbranchus Martynov and Korshunova, 2025, Nudibranchus Martynov, 1998, reinstated, and Produnga Martynov, 1998, reinstated. See brief genus-level diagnoses below. Remarks: The family Eubranchidae represents an outstandingly unique taxon within the superfamily Fionoidea, because on one hand it clearly morphologically represents the only survived fionoidean family with the ancestral triserial radula, but on the other hand, Eubranchidae are robustly placed within the otherwise uniserial superfamily Fionoidea as sister to the majority of other families (except Abronicidae) according to the molecular phylogenetic data (Figs 1, 2; see Synopsis above). Thus the mutilevel, complex nature of the family Eubranchidae, which from one view is definitely more morphologically ‘ related’ to other triserial superfamilies, but from the viewpoint of the particular, otherwise exclusively uniserial, superfamily Fionoidea (Fig. 2) is the self-evident example that any lumping approach in taxonomy will undermine the correct presentation of the underlying complex evolutionary pathways. When pan-lumping logic is arbitrarily applied at the family-level, the remarkable genus-level diversity of external morphology, radula, and reproductive apparatus, which has previously been documented in detail (Martynov 1998, 2005, Korshunova et al. 2020 b) within the family Eubranchidae, is fundamentally wiped out under the diagnoses-less and extremely heterogenous so-called genus ‘ Eubranchus ’. On the contrary, for example, every small detail in almost all possible combinations of external, radular, and reproductive system morphology are employed to produce numerous genera within the family Facelinidae, commonly with a few species per genus or monotypic (WoRMS 2024). In the course of our morphological revision of the family Eubranchidae, all major groups have been revealed and clearly recognized taxonomically. For example, ceratal branch morphology, radular patterns, and morphology of the copulative apparatus, especially the latter, as in the family Facelinidae, may be dramatically different between various Eubranchidae genera (Martynov 1998). In addition, the molecular data (Korshunova et al. 2020 b), which show paraphyly of some even narrowly defined genera, by no means imply that all Eubranchidae diversity must be lumped under the so-called ‘ single genus “ Eubranchus ” ’. In that respect, it has previously been shown in detail that the type species of the genus Eubranchus, E. tricolor, fundamentally and very distinctly differs from all known representatives of the family in the possession of strongly branched rows of the digestive gland and placement of the supplementary gland in the male reproductive system, which inserts into the vas deferens and not into the penis (Martynov 1998, Korshunova et al. 2017 c, 2020 b, Martynov and Korshunova 2025). This combination of characters is unique for the single true genus Eubranchus, and, therefore, none of the more than 50 species currently assigned to the alleged ‘ genus Eubranchus ’ can be reliably assigned to the real, proper genus Eubranchus (restricted to only the type species E. tricolor), the stem-genus name of the family Eubranchidae. These morphological patterns are drastically different from all other Eubranchidae, and cannot be ignored. Therefore, at the present time, a maximally possible, major genus-level Eubranchidae diversity is delineated, but an exhaustive species-level synopsis is not given, because several undescribed genera still need to be separated. However, any of the Eubranchidae taxa that cannot be assigned to any of the currently recognized genera, can also not be considered as belonging to the genus Eubranchus proper and must be designated in WoRMS and other sources only as ‘ Eubranchus ’ in quotation marks. Therefore, the previous careful fine-scale morphological revision of genus-level taxa within the family Eubranchidae (Martynov 1998) cannot be disregarded. While for several new or uncertain species the genus-level position still needs to be assigned (including separation of more new genera), it is urgently necessary to return a finely differentiated taxonomy to the family Eubranchidae, because currently the majority of the disparate diversity within Eubranchidae is unfortunately synonymized with the extremely heterogenous genus ‘ Eubranchus ’, where some genera are chaotically retained as valid, others are not, thus profoundly ignoring previous well-documented morphological and molecular differences (Martynov 1998, 2005, Martynov and Korshunova 2011, Korshunova et al. 2017 c, 2020 b). Especially remarkable is the diversity of the uniquely constructed, strongly differentiated copulative stylets (in length, proportion, and number) along with a reduction of the true penis within the genera Aenigmastyletus, Dunga, and Leostyletus (see: Martynov 1998, 2005). Such specially differentiated stylets and the absence of a true penis are an absolutely unique pattern among all families of the suborder Aeolidacea, and, therefore, to include these taxa in the super-heterogenous, pan-lumping genus ‘ Eubranchus ’ sensu latissimo, will not merely mask that overwhelming diversity, but intentionally conceal it. Accordingly, the following genera are reinstated or confirmed as valid, because main diagnoses have been already provided in Martynov (1998) and Korshunova et al. (2020 b) and, therefore, are presented here in a brief form: Eubranchus Forbes, 1838 (restricted to only its type species E. tricolor Forbes, 1938 and any potential closely related hidden diversity). Genus diagnosis is ‘ ceratal rows strongly branched, not in regular rows, rhinophores smooth, central teeth of radula with compressed cusp, prostate not distinct, supplementary gland inserts into vas deferens, penis conical, unarmed, distal seminal receptaculum present’.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA2FFC7FC55F93DFBACF884.taxon	description	Amphorina Quatrefages, 1844, validity confirmed and species composition restricted in Korshunova et al. 2020 b and herein [type species A. farrani (Alder and Hancock, 1844) (= A. alberti Quatrefages, 1844)]. Genus diagnosis is ‘ up to six pre-anal ceratal rows (commonly up to four), rhinophores smooth, central teeth of radula with compressed cusp, prostate readily distinct, penis conical, usual penial stylet present, distinct, supplementary gland inserts into penis, distal seminal receptaculum present’, including at least the following species: A. andra Korshunova et al., 2020, reinstated, A. farrani (Alder and Hancock, 1844), A. linensis (Garcia-Gomez et al., 1990), A. pallida (Alder and Hancock, 1842), and A. viriola Korshunova et al., 2020, reinstated in its original sense, and? Amphorina amazighi (Tamsouri et al., 2015) comb. nov .. Corruptobranchus Martynov and Korshunova, 2025, [type species C. odhneri (Derjugin and Gurjanova, 1926)]. Genus diagnosis is ‘ up to 4 – 6 pre-anal ceratal rows, rhinophores smooth, central teeth of radula with non-compressed to weakly compressed cusp, prostate moderately distinct, penis conical, usual penial stylet present, indistinct, supplementary gland inserts into penis, distal seminal receptaculum present’, besides the type species, includes at least C. odhneri (Derjugin and Gurjanova, 1926), C. malakhovi (Ekimova et al., 2021), and C. sanjuanensis (Roller, 1972). Eubranchopsis Baba, 1949, reinstated (type species Eubranchopsis virginalis Baba, 1949). Genus diagnosis is ‘ two pre-anal ceratal rows, cerata with conspicuous soft spines and tubercles, rhinophores smooth, central teeth of radula with compressed cusp, prostate distinct, penis conical, usual penial stylet present, distinct, supplementary gland inserts into penis, distal seminal receptaculum present’, hidden diversity exists.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA2FFC7FC55F93DFBACF884.taxon	description	Nihonbranchus Martynov and Korshunova, 2025 [type species N. horii (Baba, 1960)]. Genus diagnosis is ‘ up to 2 – 3 pre-anal rows, rhinophores smooth, central teeth of radula with compressed cusp, prostate distinct, penis conical, usual penial stylet present, distinct, supplementary gland inserts into penis, distal seminal receptaculum present’. Eubranchulus Martynov and Korshunova, 2025 (type species E. durrelli Martynov and Korshunova, 2025), besides the type species, also includes at least Eubranchulus rupium (MØller, 1842) (= ‘ Galvina ’ olivacea O’Donoghue, 1922) and Eubranchulus novik (Grishina et al., 2024). Genus diagnosis is ‘ two pre-anal ceratal rows commonly, rhinophores smooth, central teeth of radula with compressed cusp, prostate not distinct, penis conical, usual penial stylet present, indistinct, supplementary gland inserts into penis, distal seminal receptaculum present’. In Toso et al. (2024: 9), two species, Amphorina andra Korshunova et al., 2020 and Amphorina viriola Korshunova et al., 2020, were confused and unsustainably synonymized under the name A. viriola Korshunova et al., 2020 without any analysis. This action was erroneous and completely inconsistent with the original descriptions of A. andra (Korshunova et al. 2020 b: 30 – 4) and A. viriola (Korshunova et al. 2020 b: 27 – 30). Here both original names are restored according to Korshunova et al. (2020 b). Amphorina viriola Korshunova et al., 2020 is reinstated here with restored diagnosis as: ‘ Body up to around 12 mm; large dorsal pigment spots, if present, yellow orange, dull; in specimens with yellow-orange spots on body and cerata there is never any yellow-orange pigment spot or stripe on the tail, but there might be a median whitish line or broken line on the tail; completely pale specimens lack tail spot; light pinkish subapical ring on cerata present; absence of white punctuated line on external edge of foot; cerata commonly moderate in width without distinctly attenuated apices; digestive gland in cerata relatively broad without distinct short branches; up to four anterior rows of cerata; radular formula 31 – 47 × 1.1.1, copulative stylet relatively long and almost straight, at the top, receptaculum seminis pear-shaped with short distinct stalk between reservoir and long base’. Amphorina andra Korshunova et al., 2020 is reinstated here with restored diagnosis as: ‘ Body up to at least 20 mm; large dorsal pigment spots, if present, bright yellow-orange or reddish orange; in specimens with yellow-orange or reddish spots on dorsal side and cerata, there is never any yellow-orange spot or stripe on the tail, but there could be a whitish median line on the tail; completely pale specimens lack tail stripe or spot; light pinkish subapical ring on cerata absent; absence of a punctuated white line or row of dots on the edge of foot; cerata commonly moderate in width without distinctly attenuated apices; digestive gland in cerata relatively broad without distinct short branches; up to four anterior rows of cerata; radular formula 30 – 37 × 1.1.1, copulative stylet very short and conical, receptaculum seminis subcircular with long distinct stalk between reservoir and rapidly widening base’. First, we must highlight the correct spelling of the species A. andra Korshunova et al., 2020 [not to be confused with the erroneously renamed ‘ A. viriola ’ in Tosa et al. (2024) not Korshunova et al. (2020 b)] and reinstate its original status. Amphorina andra differs from its sister-species, A. farrani, by molecular phylogenetic data and fine-scale morphological patterns (Korshunova et al. 2020 b). Amphorina andra inhabits full-saline environments, whereas A. viriola inhabits predominantly specific semi-brackish environments under the influence of the Baltic Sea, and displays significant differences in coloration from A. andra. Amphorina viriola Korshunova et al., 2020 (original status reinstated) was described in significant details to specifically highlight the fine-scale epigenetic differences of particular groups of Amphorina specimens. Therefore, any potential variations from distantly placed geographic regions (Toso et al. 2024), and, moreover, any reference to the absence of distinct genetic distances between A. andra and A. viriola, are completely irrelevant for this case and cannot be the basis for justification of synonymy of A. andra and A. viriola. In this respect, it must be noted that ICZN (1999) does not regulate or set any rules on whether one applies morphological or molecular phylogenetics in taxonomic work, and does not set any restriction for the method of separation of species if, for example, they only differ by epigenetic-driven differences in a particular region, as in the case of A. andra and A. viriola, and therefore the original status of A. viriola is restored here. Thus, the family Eubranchidae, uniquely among members of the superfamily Fionoidea, represents a complete multilevel spectrum, from possessing an ancestral triserial radula (see above justification of its ancestral status for a majority of the suborder Aeolidacea), which is invariably present without exception in all of the taxa of the family Eubranchidae, to displaying an astonishing genus-level diversity in external features and reproductive systems. This diversity is currently obscured (WoRMS 2024) under the incorrectly applied ‘ Eubranchus ’ name, and further, missing both distinct genetic and soft epigenetic differences at the ‘ species’ level, which would reveal true evolutionary patterns. Therefore, the major Eubranchidae diversity patterns are carefully revisited here, and the previously justified fine-scale taxonomy (Martynov 1998, 2005, Korshunova et al. 2020 b), both at the genus and ‘ species’ levels, is reinstated.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF94FFF7FEE5FCECFE2AFEC4.taxon	description	(Figs 1, 2; Table 4) Subfam. Facelininae Bergh 1889: 213.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF94FFF7FEE5FCECFE2AFEC4.taxon	diagnosis	Diagnosis: Body moderate to narrow. Notal edge commonly completely reduced or some lateral extensions formed. Cerata without distinct elevations, commonly numerous per row. Ceratal rows simple, arched, or branched. Rhinophores smooth, annulate, perfoliate, papillate, or covered with complex folds and wrinkles. Anus commonly cleioproctic, rarely acleioproctic or pleuroproctic. Masticatory edges of jaws moderately denticulated with single or more rows of blunt or sharpened denticles, sometimes partly compound, or smooth. Radula formula 0.1.0. Central teeth with largely non-compressed, but sometimes compressed, cusp, rarely pectinate. Distal and proximal receptaculum seminis or only proximal receptaculum. Vas deferens long to short, prostate indistinct or distinct. Accessory gland absent or present. Massive external permanent penial collar absent. Penis internal, narrow, or broad, unarmed or armed with several or single stylets or spines, sometimes partly glandular, in addition can be covered with various papillae, flaps or lobes. Genera included: Adfacelina Millen and Hermosillo, 2012, Algarvia Garcia-Gomez and Cervera, 1990, Amanda Macnae, 1954, Anetarca Gosliner, 1991, Antonietta Schmekel, 1966, Austraeolis Burn, 1962, Bajaeolis Gosliner and Behrens, 1986, Burnaia Miller, 2001, Caloria Trinchese, 1888, Cratena Bergh, 1864, Dicata Schmekel 1967, Echinopsole Macnae, 1954, Emarcusia Roller, 1972, Facelina Alder and Hancock, 1855, Facelinopsis Pruvot-Fol, 1954, Hermosita Gosliner and Behrens, 1986, Herviella Baba, 1949, Janssonius Ortea and Moro, 2022, Jason Miller, 1974, Learchis Bergh, 1896, Moridilla Bergh, 1888, Myja Bergh 1896, Noumeaella Risbec, 1937, Palisa Edmunds, 1964, Pauleo Millen and Hamann, 1992, Phidiana Gray, 1850, Pruvotfolia Tardy, 1969, Pteraeolidia Bergh, 1875, Sakuraeolis Baba, 1965, and Setoeolis Baba and Hamatani, 1965. Remarks: The family Facelinidae, even in a restricted sense (Martynov et al. 2019), with perhaps the largest composition by genus-level within the suborder Aeolidacea and an almost maximally possible number of genera, well demonstrates the profound relativeness of the still currently employed typological taxonomic methods rooted in the basically anti-evolutionary works by Linnaeus (e. g. 1758), that persist in the apparently strictly ‘ phylogenetic’ era. The diagnoses of so many genera represent the finest level of morphology-based differentiated taxonomy. So the question is why, on the one hand, are genera allowed that include only a few species per genus or monotypic (e. g. Millen and Hamann 1992, Millen and Hermosillo 2012, Gosliner et al. 2015) in one family, but on the other hand obvious and undisputable morphological and molecular diversity is completely denied or suppressed within, for example, the superfamily Flabellinoidea (Gosliner and Griffiths 1981, Gosliner et al. 2015) or the family Coryphellidae (Ekimova et al. 2022). Simultaneously keeping the numerous finely differentiated Facelinidae genera, and the fundamentally typology-based anti-evolutionary style that implies, while using various completely non-scientific arguments to make a decision such as ‘ didactic simplicity’, ‘ tradition’, ‘ usage by some putative “ authority ” ’ (e. g. Epstein et al. 2018, Gosliner et al. 2018) for the validity of a taxon, is both illogical and counter to actual evolutionary processes. If we really want to see systematics (taxonomy) as a true science, not as some branch of subjective and seemingly random decision-making, then we must follow the true mosaicism of evolution and not decide that something is ‘ oversplit’ when the conclusions are non-traditional or inconvenient for humans. That is why the term ‘ splitters’, along with the entire ‘ splitter-lumper’ unpleasant dichotomy [see especially the case described by Willan (2021) for oyster taxonomy; see also Discussion], must be completely removed from scientific arguments (Korshunova et al. 2022). And as we thoroughly argued previously and throughout the present study, the only scientific alternative to the ‘ policy-based’ non-scientific bias in current taxonomy is the use of maximal fine-scale taxonomic differentiation, where finer and finer scale morphological and molecular groups must be not disregarded, but instead recognized to a maximal degree (Figs 1, 2). While this methodology, as in any scientific endeavour, is not free from problems and inconsistencies (see: Korshunova et al. 2022), it is the only reliable alternative to the currently commonly employed manner of doing taxonomy — when a phylogenetic tree is obtained, based on some not always clearly explained taxon selection, and some apparently monophyletic groups are afterwards detected, then the ‘ taxonomic arrangement’ of how many ‘ species’, genera, families, and so on to be recognized is matter of largely non-evolutionary, non-scientific argumentation of ‘ general policy in a given group’, plainly understood ‘ usability’, and, ultimately, ‘ authority-approval’. All these highly archaic and cautious-sounding (but still persistent in taxonomy at a practical level) ‘ set of methods’ must definitely be changed if we really want a coherent future for both our very old and very modern, basic biological science of systematics (taxonomy). The family Facelinidae in its current genera composition is obviously still too heterogenous, both at a morphological and a molecular level, even after removing the families Myrrhinidae (Martynov et al. 2019) and Favorinidae (present study; Figs 1, 2), and definitely more family-level taxa need to be recognized within the current ‘ Facelinidae s. l. ’.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF95FFF5FF07FB8BFB56FB1D.taxon	description	(Figs 1, 2; Table 4)	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF95FFF5FF07FB8BFB56FB1D.taxon	diagnosis	Diagnosis: Body narrow. Notal edge completely reduced. Anterior cerata in distinct arches, posterior ceratal rows in arches and rows. Rhinophores with swellings or smooth. Anus cleioproctic. Masticatory edges of jaws moderately denticulated. Radula formula 0.1.0. Central teeth with reduced denticles, or denticles absent, cusp non-compressed. Distal and proximal receptaculum seminis. Vas deferens moderately long to short, prostate indistinct or distinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, not considerably widened, unarmed. Genera included: Favorinus Gray, 1850. Remarks: The family Favorinidae, reinstated, is well characterized by the combination of central teeth of radula with predominantly reduced to completely absent denticles, rhinophores commonly with swellings instead of lamellae or papillae, and ark-shaped, anterior ceratal rows. Its distinctness was recognized by Bergh (1889) and further several taxonomists had considered that family as valid (e. g. Odhner in Franc 1968, Thompson and Brown 1984). Recently, the family Favorinidae has been recovered as valid in several analyses and it was shown that favorinids represent an ancestral group for the evolutionary formation of the highly aberrant pleistonic Glaucidae (Goodheart et al. 2018, Martynov et al. 2019, Colin et al. 2024, present study; Figs 1, 2). However, in WoRMS (2024) this family is still considered, for some unclear reason, as ‘ unaccepted’. Importantly, if Favorinidae Bergh, 1889 were synonymyzed with Facelinidae Bergh, 1889, then it must be formally synonymyzed (see below) with its sister, again, the profoundly aberrant family Glaucidae Gray, 1827. Furthermore, the family Glaucidae Gray, 1827, which is drastically different from all taxa of the suborder Aeolidacea, was established on the same date with the ‘ type’ for the entire Aeolidacea family Aeolidiidae Gray, 1827. Thus, a cascade of unsubstantiated family-level synonymyzation will inevitably ruin any taxonomic structure within the suborder Aeolidacea. We, therefore, formally restore the family Favorinidae Bergh, 1889, reinstated, and again reiterate that if one finely differentiated taxon vanishes due to lumping at any level — including genera and families — almost all other families (e. g. all families within the superfamily Aeolidioidea) could also potentially be lumped into each other such that only one of two of the oldest families, Aeolidiidae Gray, 1827 or Glaucidae Gray, 1827 would be left. To avoid this highly inconsistent action, both from a morphological and a molecular perspective, finely differentiated taxa should be maintained to the maximal degree possible. In fact, more families, even within the restricted Facelinidae (Martynov et al. 2019), still need to be separated and restored in the future.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9AFFFAFEC1FF05FD91F9A0.taxon	description	(Figs 1, 2; Table 4) Gray 1857: 227.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9AFFFAFEC1FF05FD91F9A0.taxon	diagnosis	Diagnosis: Body wide. Notal edge present. Ceratal rows branched, numerous non-elevated cerata per row. Membranaceous fold on ceratal edge in the type genus. Rhinophores smooth. Anus cleioproctic. Masticatory edges of jaws commonly bear single row of simple or compound denticles. Radula formula 0.1.0. Central teeth usually with strong cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens extremely long, prostate indistinct. Supplementary gland absent. Massive external permanent penial collar absent. Penis internal, extremely long, narrow, unarmed. Genera included: Fiona Alder and Hancock, 1853 and? Tergiposacca Cella et al., 2016 (temporarily included). Remarks: Choosing the family ‘ Fionidae’ sensu latissimo as the basis for synonymizing the morphologically and molecularly hugely disparate family and genera levels of the superfamily Fionoidea lacks anything approaching even ‘ phylogenetic systematics logic’: the family Fionidae proper completely lacks the main apomorphy of the pan-lumping ‘ Fionidae’ – the supplementary gland. Throughout literature, the special supplementary gland is also inappropriately termed as ‘ penial’. This is incorrect, because the supplementary gland can be inserted either to the vas deferens, or to the base of penial sheath, and, at any measure, the supplementary gland is never a completely integral part of the penis, and, therefore, the term ‘ penial gland’ should be avoided. The other main external character of the family Fionidae — the distinct notal edge — differs not only from the more related family Trinchesiidae, but also from all other families of the superfamily Fionoidea (Korshunova et al. 2017 a, b, c, 2021, 2022), except for the strongly-reduced notal edge in the family Murmaniidae. Prior to its erroneous synonymization in 2016, for more than 150 years of taxonomic history the family Fionidae has invariably contained only a single, highly peculiar (compared to a majority of related families) genus Fiona (Gray 1857, Odhner in Franc 1968, Jensen 2000). The genus Tergiposacca, although also lacking a supplementary gland, otherwise is significantly different from Fionidae proper and is included in that family temporarily (Tables 3, 4).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA0FFC2FC66FD28FAFFFDBE.taxon	description	(Figs 1, 2; Tables 1 – 3) ‘ Tribe Acleioprocta’ part. Odhner 1939: 50 – 3. Diagnosis: Aeolidacean superfamily predominantly with uniserial radula, and so far includes only a single known triserial family, Eubranchidae. Notal edge commonly completely reduced, very rarely present. Cerata commonly placed in regular, simple rows, more rarely in branched rows. Anus commonly acleioproctic, rarely in cleioproctic position, and only a unique example of occasional pleuroproctic position. Anterior foot corners commonly absent, more rarely present. Commonly no elaborate oral glands, but in some taxa oral glands more distinct. Masticatory edges of jaws commonly bear a single row of simple or compound, sharpened or tubercle-like denticles, rarely several rows. Central teeth cusp commonly not compressed, rarely compressed by adjacent lateral denticles. Lateral teeth, if present, usually smooth. Commonly single distal receptaculum, sometimes both proximal and distal seminal receptaculums. Clasping organ in female part of reproductive system absent. Vas deferens usually short to moderate, prostate indistinct to distinct. Special supplementary gland in the male part of reproductive system present in all known families, except for the stem-bearing name Fionidae. Other accessory glands absent. Massive external permanent penial collar absent. Penis internal, of various patterns, but commonly not considerably widened; in several families usually with well-defined hollow stylet, or stylet system is considerably modified, in other families penis unarmed. Families included: Abronicidae Korshunova et al., 2017, Eubranchidae Odhner, 1934, Murmaniidae Korshunova et al., 2017, Xenocratenidae Martynov et al., 2020, Cuthonellidae Miller, 1971, Calmidae Iredale and O’Donoghue, 1923, Cuthonidae Odhner, 1934, Tergipedidae Bergh, 1889, Fionidae Gray, 1857, and Trinchesiidae Nordsieck, 1972. Remarks: The taxonomic volume of the superfamily Fionoidea is restricted here [with the removal of the obviously flabellinoidean Coryphellidae and Paracoryphellidae (WoRMS 2024), as well as any other non-related families; see Synopsis above and below and Fig. 1], to the core monophyletic predominantly uniserial (triserial only in one family, Eubranchidae) families with a distinct supplementary gland present in the majority of families, except the genus-name bearing Fionidae proper. The superfamily Fionoidea (Figs 1, 2) currently is among one of the most finely-differentiated major aeolidacean super-groups in which fine-scale morphological and molecular data are most consistently conjoined, although more families potentially need to be separated (see: Korshunova et al. 2017 a – c, 2019 a, 2021, 2022, Martynov et al. 2019, 2020). However, there are continuous attempts to dismissively lump all Fionoidea superfamily diversity into a single ‘ family Fionidae’ (e. g. Kim et al. 2024), despite substantial morphological and molecular arguments. To do so immediately implies that we must lump all of the nearly 30 families of the suborder Aeolidacea into a single family, Aeolidiidae Gray, 1827 / Glaucidae Gray, 1827, because almost all major characters that are known for the superfamily Fionoidea can potentially be found in other superfamilies (see Synopsis above and below). Particularly, an acleioproctic anus, one of the most common characteristic features of Fionoidea in many taxa, has been reported for some taxa within the superfamilies Apataoidea, Cumanotoidea, Aeolidioidea, and Flabellinoidea. At the same time, within Fionoidea there are instances of a definitely cleioproctic anus, among the Murmaniidae, Cuthonellidae, and Cuthonidae families, which is in turn common for the superfamily Aeolidioidea. Along with common cleioproctic anus, the latter superfamily may in turn rarely include a pleuroproctic anus, which is very common within superfamily Flabellinoidea. The regular ceratal rows, also characteristics for Fionoidea, are also present in Apataoidea and some of Aeolidioidea. As previously confirmed (Korshunova et al. 2017 a), and in the present study (Fig. 2), the uniserial radula, one of the key characters within Aeolidacea, originated based on the reduction of the triserial radula, possibly no less than four (and may be more) times independently in the course of the evolution of the suborder Aeolidacea (Fig. 1; Tables 1, 2). Therefore, every apparently exclusively uniserial superfamily of the suborder Aeolidacea may actually or potentially include triserial families as part of its ancestral diversity, which is well-highlighted in the phyloperiodic tables [Tables 1, 2; see details of building of Phyloperiodic Tables in Martynov and Korshunova (2022) and, Korshunova and Martynov (2024)]. Remarkably, in the present study we report the crucial discovery of the uniserial family Hantazuidae fam. nov., which is robustly placed within the otherwise triserial superfamily Flabellinopsoidea (see Synopsis below; Figs 1, 2; Tables 1, 2), thus uncovering a confirmed example of the independent reduction of the triserial radula into a uniserial one (Fig. 1). The triserial families are so far firmly confirmed for a majority of the aeolidacean superfamilies, except Unidentioidea and Aeolidioidea (Fig. 2; Tables 1 – 3). In this respect, the new family Chudidae fam. nov., described in the present study, may potentially present a ‘ missing evolutionary link’ of the yet unknown, but definitely existent, triserial ancestor of the superfamily Aeolidioidea. But because Chudidae fam. nov. are also sister to the superfamilies Cumanotoidea, Aeolidioidea, Flabellinopsoidea, and Flabellinoidea, we prefer to establish the superfamily Chudoidea superfam. nov. (see Synopsis below; Figs 1, 2; Tables 1, 2) for the new family Chudidae fam. nov. In many respects, the triserial superfamily Chudoidea superfam. nov. demonstrates affinities to both the predominantly triserial superfamilies Cumanotoidea, Flabellinoidea, Flabellinopsoidea, and to the exclusively uniserial Aeolidioidea, and its discovery uncovers this evolutionary highly important taxon, which has partly preserved its ancestral features, including a triserial radula. Remarkably, the superfamily Fionoidea robustly includes precisely the triserial family Eubranchidae (Korshunova et al. 2017 a, 2020 b, 2021, present study; Figs 1, 2), which unequivocally suggests that potentially a triserial ancestral family can be discovered (see Phyloperiodic Table, 1) in any superfamily, even in a completely uniserial modern superfamily of the suborder Aeolidacea. Therefore, in spite of the fact that all previously provided arguments are more than enough evidence for the unavoidable necessity of the family-level fine-scale differentiation among the superfamily Fionoidea, as well as in any other aeolidacean superfamilies (present Synopsis, Fig. 2), the strong bias and ad hoc preconceptions for lumping of all finely-differentiated families of the superfamily Fionoidea into putatively a ‘ single family’ still persists (see details and discussion in: Korshunova et al. 2021, 2022). Instead, and simultaneously, equally strong preconceptions persist for the ‘ necessity’ of several families and truly numerous genera only within the superfamily Aeolidioidea (see details and references in Synopsis below; Figs 1, 2), but for some unsubstantiated reasons are not allowed within the superfamily Fionoidea or the flabellinoidean family Coryphellidae (see Synopsis below, and Discussion; Figs 1, 2). Therefore, we propose herein, that if, for example, one lumps the distinctly triserial family Eubranchidae into the ‘ single family Fionidae’ instead of placing it within the fine-scale family system of the superfamily Fionoidea (Fig. 2), one should also, without any hesitation, lump all of the nearly 30 families of the whole suborder Aeolidacea into just a single family (see also details in Discussion). Triserial families, again, are present in the absolute majority of aeolidacean superfamilies over the whole molecular phylogenetic tree of the suborder Aeolidacea (Fig. 2), and all supposed ‘ intermediate’ states can be potentially ‘ designated’ between the majority of existent families. Thus, the preconception against truly evolutionary morphological and molecular arguments, and the persistent denying of fine-scale family level differentiation within the superfamily Fionoidea, clearly show an adherence to an undefined ‘ taxonomic-policy’. The even more remarkable lumping case of the family Fionidae proper (a family fundamentally based mainly on the characters of the stem-genus Fiona, and not from the majority of other Fionoidea families) is connected not only with those who deny fine-scale taxonomic differentiation, but also with the still commonly employed cladistic principle of searching for ‘ apomorphies / synapomorphies’. Because when pan-lumping the morphologically unmanageable assemblage of the putative ‘ Fionidae sensu latissimo ’ was suggested, an ‘ apomorphy-based diagnosis’ was proposed, which unambiguously included the ‘ presence of a “ penial ” gland’. Ironically in that case, however, the very genus Fiona Alder and Hancock, 1853 does not possesses any ‘ penial’ gland in the reproductive system. (see details in: Korshunova et al. 2017 c, 2021, 2022). That case, therefore, not only refutes the strong ‘ pan-lumping bias’ in a particular nudibranch superfamily, Fionoidea, but also undermines apomorphy-based taxonomy, one of the most seemingly fundamental principles in contemporary taxonomy. Thus, there must now be a complete ‘ full stop’ to any further attempts to dismissively lump the fine-scale Fionoidea (and other superfamilies) family diversity (Synopsis above and below; Figs 1, 2; Tables 1 – 4). However, a very important conclusion, both theoretical and practical, needs to be made that has relevance not only for the particular ‘ nudibranch case’ made here, but without exception for all diversity-based studies of all living organisms. Because it is clear that any attempts to comprehend the simultaneously highly irregular and partly regular in some sense (see: Martynov and Korshunova 2022) evolutionary process, which has resulted in the appearance of astonishing diversity, in all its multilevel scale, from the smallest molecules to morphologically distinct individuals and their groups, cannot be truly understood using only such typological seemingly ‘ strict’ diagnoses of classic anti-evolutionary taxonomy (still in operation), or ‘ strictly defined’ apomorphies of even apparently ‘ evolutionary’ phylogenetic taxonomy. In opposition to the pan-lumping scenario, here we present proof of the profound mosaicism of diagnoses at almost every level, from the Aeolidacea suborder to each individual genus, including the fundamental absence of any ‘ completely clear and distinct from other taxa’ diagnosis. But at the same time we highlight several obvious quasi-regular general trends caused by the common ancestral ontogenetic basis, such as, for example, distribution and proportions of the triseral and uniserial families within the superfamilies of the suborder Aeolidacea (see Synopsis; Figs 1, 2; Tables 1, 2), coupled with fundamentally blurred borders of all taxa even in the most ‘ complete’ phylogenomic analyses, including ‘ species’ and order levels, e. g., in Karmeinski et al. (2021), where the position of a single nudibranch family, Embletoniidae, has been ‘ blurred in between’ the otherwise taxonomically distinct suborder Aeolidacea and ancestral non-aeolidaceans, even using applied transcriptomic analysis. Or in Coates et al. (2018), where blurred borders between ‘ population’ and ‘ species’ categories have been shown, and there is no doubt that an absence of clear borders between ‘ species’ and ‘ populations’ is characteristic for any group of organisms, including nudibranchs (Korshunova and Martynov 2024). In other words, because the fundamentally dynamic nature of evolution in all its genetic and epigenetic totality is the principle underlying any true taxonomy, any taxon can never be made as clear and distinct as it has claimed to have been made over many centuries within the basically anti-evolutionary classic taxonomy, but we must still unavoidably use those methods while producing taxonomic systems. Likewise the relative and practical problems of ‘ phylogenetic systematics’, which is also a rigidly proposed set of strict rules — such as the strict distinction of plesiomorphies and apomorphies (Hennig 1966) — especially from the point of view that any organism represents not ‘ phylogenetic lineages’ but an individual dynamic, interacting, evolving ontogeny, has been already pointed out (see e. g. Martynov and Korshunova 2022). Therefore, we are facing current multiple crises, both in society and in science, particularly in biological systematics, where the old ‘ structure of science’ has been largely undermined by the current ‘ molecular phylogenetic era’. But new paradigms are only at the emerging stage, and we must remember that when we make a taxonomy / classification of any organism, we are dealing not with static preserved organisms in museums or even living organisms seeming to appear in relatively ‘ static’ modern ecosystems, but with finely-differentiated organismal diversity that has been formed on the basis of very complex, constantly dynamic, multilevel, and clearly not strictly regular evolutionary processes. Therefore, any taxonomic arrangements or systems that pretend to be maximally aligned with those evolutionary processes, must be equally complex, not strictly regular or seeking an ‘ absolute distinctness at the level of diagnoses’, and they must be unavoidably finely-differentiated regarding ‘ subordinate taxa’, whose numbers must not be restricted by any ad hoc preconceptions such as ‘ simplicity’ or ‘ didactic usefulness’ but only by the endlessly evolutionary-based organismal forms.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF1FF90FC98FEF1FE76FDDE.taxon	description	(Figs 1, 2, 13; Table 5) Korshunova et al. 2017 a: 29 – 30. Type species: Aeolis lineata Loven, 1846. Diagnosis: Body moderately narrow. Notal edge present, discontinuous. Cerata in several groups. Rhinophores smooth. Anterior foot corners present. Central teeth with non-compressed narrow cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into a broad penial sheath, prostate indistinct. Penis broad, lobe-shaped. Species included: Fjordia browni (Picton, 1980) comb. nov., Fjordia capensis (Thiele, 1925) comb. nov., Fjordia lineata (Loven, 1846) comb. nov, Fjordia chriskaugei Korshunova et al., 2017 comb. nov., and Fjordia (?) insolita (Garcia-Gomez and Cervera, 1989) comb. nov. Detailed morphological data for Fjordia browni, F. lineata, and Fjordia chriskaugei are presented in Korshunova et al. (2017 a). Remarks: The newly added Fjordia capensis forms a separate clade within Fjordia, sister to F. browni, F. chriskaugei, and F. lineata (Figs 1, 13). The genus Fjordia invariably forms a distinct, stable phylogenetic group (Figs 1, 2, 13) and morphologically is differentiated from any coryphellid genera by a combination of the presence of a discontinuous notal edge, relatively weak cusp of the central teeth, and very short vas deferens. The phylogenetically sister-genus Gulenia readily differs from Fjordia by the stable presence of a continuous notal edge and stronger cusp of the central teeth (see below). The genus Fjordia remarkably encompasses several species over quite a large biogeographic range in the NE Atlantic from temperate South Africa (Fjordia capensis) to Norway and the UK (Fjordia lineata, F. browni, and F. chriskaugei), but fundamentally keeps essential morphological similarity and molecular unity (Figs 1, 2, 13). Importantly, the placement of the South African species F. capensis (original description in: Thiele 1925) within Fjordia was predicted using only morphological data in Korshunova et al. 2017 a because molecular data for F. capensis was not available at that time. Coryphellidae taxa precisely predicted to their particular fine genus-levels by morphological data in 2017 are indicated by tick marks in Figure 13 with molecular data profoundly confirming that placement appearing significantly later (Ekimova et al. 2024) under the pan-lumping name ‘ Coryphella ’. This is clear evidence for the validity of both the fine-scale morphological approach and fine-scale genus- and family-level taxonomic differentiation. Interestingly, the sister to the Fjordia genus, Gulenia, is so far restricted exclusively to the Norwegian coast and partly adjacent waters of Denmark and Sweden. In other words, it is clearly restricted to Scandinavian waters, compared to the much broader distribution of the genus Fjordia, which encompasses both the northern and southern Atlantic Ocean. In that respect, since the genus Gulenia is characterized by the ancestral feature of a continuous notal edge, unlike the broader distribution of Fjordia with its discontinuous, partly reduced notal edge, it may suggest that the restricted distribution of the genus Gulenia represents a relic of an initial evolutionary radiation of an ancestral taxon of the genera Gulenia and Fjordia, which, therefore, probably had a continuous notal edge. Comparison of the genus Fjordia with all valid, currently included Coryphellidae genera is presented in Table 5. All these data and results well highlight the reliability and obvious necessity of fine-scale taxonomic differentiation for careful documentation of both large- and small-scale evolutionary changes.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8EFFEEFF4EF954FA45FA02.taxon	description	(Fig. 1, 2; Tables 1 – 3) ‘ Tribe Pleuroprocta’ part. Odhner 1939: 50 – 3. Diagnosis: Aeolidacean superfamily with triserial radula. Notal edge commonly present, either continuous or discontinuous, more rarely almost completely reduced. Cerata are not placed in regular rows, but are placed either in continuous, irregular rows, or discontinuous groups, or may be placed on stalk-like notal derivation in correlation with a continuous or discontinuous notal edge. Anus commonly pleuroproctic, rarely mixed pleuroproctic toward acleioproctic / cleioproctic position. Anterior foot corners commonly present. Elaborate oral glands commonly absent, more rarely present. Masticatory edges of jaws in many taxa bear several rows of compound, sharpened or tubercle-like denticles. Both proximal and distal seminal receptaculums are commonly present, more rarely reduced to single one. Clasping organ in female part of reproductive system absent. Vas deferens more commonly moderately long, but can be also very short, prostate indistinct or distinct, including highly elaborated one. Supplementary gland or usual accessory glands are completely absent. The only known example of a wellpronounced accessory gland protruding from the penial base is in the genus Occidenthella of the family Coryphellidae, which was formed completely independently from the superfamilies Fionoidea and Aeolidioidea. Massive external permanent penial collar present in the genus Chlamylla of Paracoryphellidae, commonly absent. External penis present in the genus Paracoryphella of Paracoryphellidae, commonly penis internal, devoid of any cuticular structures. Families included: Paracoryphellidae Miller, 1971, Flabellinidae Bergh, 1889, and Coryphellidae Bergh, 1889. Remarks: The superfamily Flabellinoidea Bergh, 1889 is reinstated here following our molecular phylogenetic analysis, which robustly places the core triserial families Flabellinidae Bergh, 1889, Paracoryphellidae Miller, 1971, and Coryphellidae Bergh, 1889 into a highly supported monophyletic group (Figs 1, 2). The superfamily Flabellinoidea is solely comprised of triserial families without confirmed exceptions so far. Most of the taxa of the superfamily Flabellinoidea possess a notal edge that is continuous, discontinuous, or modified into stalks, and the reproductive system is devoid of any cuticular stylets. Supplementary gland is always absent, but in one genus Occidenthella of the family Coryphellidae, there is a clearly convergently-formed accessory gland protruding from the penial sheath (see detailed genus-level Synopsis of the family Coryphellidae genera below).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF89FFE9FF2DF929FC4EFAA4.taxon	description	(Figs 1, 2; Table 4) ‘ Genus Flabellina sensu latissimo ’ Gosliner and Griffiths 1981: 105, 109 – 15.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF89FFE9FF2DF929FC4EFAA4.taxon	diagnosis	Diagnosis: Body relatively wide. Notal edge discontinuous. Cerata on broad extensions, numerous per row. Ceratal rows branched. Rhinophores perfoliate or granulate. Anus pleuroproctic. No elaborate oral glands. Masticatory edges of jaws bear several rows of compound, sharpened, or tubercle-like denticles. Radula formula 1.1.1. Central teeth usually with cusp compressed by adjacent lateral denticles. Lateral teeth narrow or with attenuated process basally, denticulated, or smooth. Distal receptaculum seminis. Vas deferens long, prostate indistinct or distinct. Supplementary and accessory gland absent. Massive external permanent penial collar absent. Penis internal, unarmed. Genera included: Flabellinopsis MacFarland, 1966 and Baenopsis Korshunova et al., 2017. Remarks: Bergh (1904) described a species ‘ Coryphella ’ californica, which is characterized by ringed (although in a preserved state) rhinophores, c. 10 ceratal groups on lateral parts of the back, and a triserial radula with numerous short lateral denticles of the central teeth. The latter character especially is contrary to any radular pattern in any genera of the proper family Coryphellidae (see: Korshunova et al. 2017 a, present study Synopsis below). The shape of the radular teeth and number of small numerous denticles (c. 17) of ‘ Coryphella ’ californica, however, closely resemble Flabellinopsis iodinea (Cooper, 1862), which inhabits essentially the same geographic region. External characters of ‘ Coryphella ’ californica, taking into consideration that Bergh described a preserved specimen, do not contradict the features described by MacFarland (1966) in the original description of the genus Flabellinopsis and its type species F. iodinea. We propose, therefore, to consider ‘ Coryphella ’ californica as a junior synonym of Flabellinopsis iodinea with a question mark. It is not a contradiction of our methodology consistently presented here, because ‘ Coryphella ’ californica is an old, semi-obscure taxon that obviously possesses a radula, which otherwise is not similar to Coryphellidae, but instead is similar to the distantly related family Flabellinopsidae. Therefore, the continuous usage of ‘ Coryphella ’ californica as a member of the family Coryphellidae will confuse real phylogeographic and taxonomic patterns of coryphellids.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF95FFF4FC01FB2EFE90FCD8.taxon	description	(Figs 1, 2; Table 4) Gray 1827: pl. 3, figs 21, 22. Korshunova et al. 2017 a: supplementary materials. Diagnosis: Body broad. Notal edge completely reduced. Cerata on extremely enlarged stalks, numerous per row. Ceratal rows simple and arched. Rhinophores smooth. Anus cleioproctic. Masticatory edges of jaws moderately denticulated with single row of irregular, blunted, or partly sharpened denticles. Radula formula 0.1.0. Central teeth with non-compressed cusp. Distal and proximal receptaculum seminis or only proximal receptaculum. Vas deferens moderately to considerably long, prostate indistinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, broad, armed with stylet or unarmed. Genera included: Glaucus Forster, 1777 and Glaucilla Bergh, 1861. Remarks: The genus Glaucus Forster, 1777 represents one of the oldest, and at the same time one of the most aberrant, taxa not only within the superfamily Aeolidioidea, but also within whole suborder Aeolidacea, because of its highly modified body form adapted to a specific pleistonic habitat (Colin et al. 2024). The remarkable nomenclatural coincidence that the family Glaucidae Gray, 1827 was established (Gray 1827) in the same year as the family Aeolidiidae Gray, 1827 (with the stem-genus bearing name Aeolidia Cuvier, 1798), makes a very unfortunate case for the supporters of pan-lumping systems in Nudibranchia because the most aberrant family Glaucidae (with the name Glaucus older than the stem-genus name Aeolidia), would become the super-lumped family ‘ Glaucidae’ (Rudman 1980), which would encompass all the possible morphological and molecular diversity of the suborder Aeolidacea [see Martynov et al. (2019) and present study, Synopsis, Remarks to the superfamily Fionoidea, and detailed explanations in Discussion]. Therefore, to avoid that action, which would obviously immediately and profoundly dismiss all suborder morphological and molecular diversity (present study, Synopsis above and below; Figs 1, 2), fine-scale differentiated taxonomy must be employed at family and genera levels not only occasionally, as for some unsubstantiated reason within the superfamily Aeolidioidea and, particularly, for the family Facelinidae (see Synopsis below) only, but consistently to all superfamilies and families of the suborder Aeolidacea, as thoroughly explained in the present study (see Synopsis and Figs 1, 2).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF0FF90FF3DFDEBFABDFDDF.taxon	description	(Figs 1, 2, 13; Table 5) Korshunova et al. 2017 a: 34. Type species: Gulenia orjani Korshunova et al., 2017. Diagnosis: Body moderately wide. Notal edge present, continuous. Cerata in continuous rows. Rhinophores smooth to wrinkled. Anterior foot corners present. Central teeth with non-compressed wide cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into a broad penial sheath, prostate indistinct. Penis broad, lobe-shaped. Species included: Gulenia borealis (Odhner, 1922) comb. nov., Gulenia monicae Korshunova et al., 2017 comb. nov., and Gulenia orjani Korshunova et al., 2017 comb. nov. Detailed morphological data in Korshunova et al. (2017 a). Remarks: Gulenia borealis, G. monicae, and G. orjani cluster with the highly-supported Gulenia clade and form a sister-group to the Fjordia clade (Figs 1, 13). The genus Gulenia differs from the phylogenetically sister-genus Fjordia by a continuous notal edge, a notable ancestral feature especially pronounced in the species Gulenia borealis (original description in: Odhner 1922). For the discussion and justification of the ancestral status of this character see Korshunova et al. (2017 a), and Martynov et al. (2020). Gulenia, along with a few other coryphellid genera, is partly similar to members of the family Paracoryphellidae, which is otherwise very different and invariably forms a distinct, compact molecular phylogenetic group (see Synopsis above; Figs 1, 13). During our extensive field work in the course of more than seven years in Gulen, Norway (the type locality of two of the Gulenia species), we observed hundreds of Gulenia specimens, but never saw any specimen with a discontinuous notal edge. It is potentially possible that a discontinuous notal edge is present in juvenile specimens, or in specimens living in some special environmental conditions (e. g. in Denmark and Sweden), but otherwise the presence of a continuous notal edge represents a stable and well-diagnosable feature in subadult and adult Gulenia. Furthermore, the central teeth of the genus Gulenia have a stronger cusp than in Fjordia. There are no other coryphellid genera that present the set of characters as found in the genus Gulenia. According to all molecular phylogenetic data, the sister-genera Gulenia and Fjordia invariably form distinct, stable, separate clades. The crucial importance of fine-scale taxonomic differentiation at the generic level is especially well illustrated by the genus Gulenia, since it includes some of the most morphologically difficult to distinguish, hidden diversity within the family Coryphellidae, represented by the species Gulenia monicae and Gulenia orjani (Korshunova et al. 2017 a). Without fine-scale taxonomic differentiation, all these differences would be obscured under the pan-lumping concepts of ‘ Flabellina ’ or ‘ Coryphella ’. Comparison of the genus Gulenia with all valid, currently included Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8FFFEEFC0FFBE1FE62F920.taxon	description	(Figs 1, 9) urn: lsid: zoobank. org: act: 07 C 10 E 38 - 8491 - 4248 - 93 AD- 5 BDFF 41 C 0848 Etymology: In honour of citizen scientist Kaoru Imagawa (今 川 郁), Japan, the chief manager of the Ocean Blue dive club in Okinawa, who greatly contributed to the present study by observing and collecting nudibranchs. Holotype: KM 1059, L = 10 mm (live), Japan, Okinawa, Arasaki, stones, 5 m depth, 30 October 2021, coll. Kaoru Imagawa. Description External morphology (Fig. 9 A – C) Body narrow. Foot and tail narrow, anterior foot corners moderate in length. Rhinophores similar in length to oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming up to about 15 – 20 small curved lobes with cerata in total (placed partly in a scallop-like pattern, if counting only the ceratal lobe-based groups, there will be correspondingly fewer in number) and separately placed cerata along dorsal edges, which are formed by a reduced discontinuous notal edge (Fig. 9 A – C). Apices of cerata gradually pointed, with elongated cnidosacs. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below middle ceratal lobes. Reproductive openings lateral, below first-second and third-fifth ceratal lobes / separate cerata. Colour (Fig. 9 A, C) Background colour semi-transparent dark greyish. Cerata distinctly zoned — opaque white for approximately two-thirds of their length and orange brownish apically. Rhinophores covered with milky-whitish pigment over almost their entire length. Apical parts of cerata without opaque cap of white pigment. The blackish ampulla shines through the anterior part of the dorsal side and is characteristically well visible in living specimens. Blackish and whitish gonad shines through the mid and posterior parts. Jaws (Fig. 9 F, G) Jaws oval-triangular. Edge of masticatory processes bears up to at least 26 denticles that may form compound row of thickened denticles comprised of some smaller tubercles. Radula (Fig. 9 D, E) Radula formula in holotype about 12 × 0.1.0. Central teeth considerably narrow, elongate-triangular, rather feather-shaped with short, narrow, commonly double cusps. Central teeth bear up to at least about 10 well-defined distinct denticles, but narrowly-arranged toward cusps. Lateral teeth absent. Reproductive system (Fig. 9 H – J) Hermaphroditic duct leads to oval, relatively large swollen ampulla. Vas deferens moderately long, narrow, somewhat convoluted, leads to very distinct, thick prostate. Penial sheath is oval. Penis is broadened conical, bears short, very slightly curved / almost straight stylet. Oviduct connects through insemination duct into female gland complex. Proximal receptaculum seminis elongate. Distal receptaculum seminis present, rather rounded, almost sessile on a short stalk. Ecology: Shallow waters, stony habitats. Distribution: In our material, present from the tropical part of Japan in Okinawa Island. Potentially may occur in other parts of the tropical regions of Japanese Islands and toward the Philippines. Remarks: Hantazuia imagawai sp. nov. externally differs from both Hantazuia yugoikedai sp. nov. and Hantazuia kimotoi sp. nov. by its paler brownish, rather than yellowish, body and ceratal coloration, and further H. imagawai sp. nov. also reliably differs from both H. yugoikedai sp. nov. and H. kimotoi sp. nov. by the shape of its copulative stylet, which is significantly shorter and almost straight, only rather slightly curved (Fig. 9 H, I). The COI uncorrected p - distances between the Hantazuia imagawai sp. nov. clade and the H. yugoikedai sp. nov., clade are 12.3 % – 12.8 %, and between the H. imagawai sp. nov. clade and H. kimotoi sp. nov. clade are 12.8 % – 13.1 %.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8FFFEFFED9FF05FC3CFBC5.taxon	description	(Figs 1, 8) urn: lsid: zoobank. org: act: 0 B 39 D 21 A- 24 F 3 - 4 F 5 F- 89 CD- D 7347 E 33 D 5 A 9 Etymology: In honour of citizen scientist Nobuhiko Kimoto (木元伸彦), Japan, the founder of a comprehensive web-site ‘ Nudibranchs of the world’ (世界のウミウシ), who most kindly helped us in observing and collecting nudibranchs. Holotype: KM 1068, L = 13 mm (live), north-western Pacific, Japan, Honshu, Jogāshima Island waters, stones, 10 – 20 m depth, 14 August 2023, coll. Yugo Ikeda. Paratype: KM 1072, L = 5 mm (live), north-western Pacific, Japan, Honshu, Jogāshima Island waters, stones, 10 – 20 m depth, 18 September 2023, coll. Yugo Ikeda. Description External morphology (Fig. 8 A – D, K, L) Body narrow. Foot and tail narrow, anterior foot corners moderate in length. Rhinophores similar in length to oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming up to about 20 – 25 small curved lobes with cerata in total (placed partly in a scallop-like pattern, if counting only the ceratal lobe-based groups, they will be correspondingly fewer in number) and separately placed cerata along dorsal edges, which are formed by a reduced discontinuous notal edge. Apices of cerata gradually pointed, with elongated cnidosacs. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below middle ceratal lobes. Reproductive openings lateral, below first-second and third-fifth ceratal lobes / separate cerata. Colour (Fig. 8 A – D, K, L) Background colour semi-transparent whitish to greyish. Cerata opaque yellowish to lemon-coloured (granulated when magnified) throughout most of the length with somewhat lighter bases. Cnidosacs in subapical parts of cerata similar in colour or slightly darker. Apical parts of cerata without opaque cap of white pigment, semi-transparent. Rhinophores covered with yellowish-whitish pigment over almost their entire length. The blackish ampulla, seminal receptacles, vas deferens and other ducts, as well as more lighter greyish thick prostate (with darker elements inside) shine through anterior part of dorsal side and are characteristically well visible in living specimens. Whitish to pinkish gonad shines through the mid and posterior parts. Jaws (Fig. 8 G, H) Jaws oval-triangular. Edge of masticatory processes bears up to at least 17 denticles that may form compound row of thickened denticles comprised of some smaller tubercles. Radula (Fig. 8 E, F, M) Radula formula in two specimens about 19 × 0.1.0. Central teeth considerably narrow, elongate-triangular, rather feather-shaped with short, narrow, commonly double cusps. Central teeth bear up to at least nine well-defined distinct, but denticles narrowly-arranged toward cusp. Lateral teeth absent. Reproductive system (Fig. 8 I, J, N – P) Hermaphroditic duct leads to oval swollen ampulla. Vas deferens moderately long, narrow, convoluted, leads to very distinct, thick prostate. Penial sheath is oval. Penis is broadened conical, bears relatively short, slightly curved stylet. Oviduct connects through insemination duct into female gland complex. Proximal receptaculum seminis elongate. Distal receptaculum seminis present, oval, almost sessile on a short stalk. Ecology: Shallow waters, stony habitats. Distribution: In our material, present from the Pacific side of middle Japan (Honshu). But according to one GenBank sequence (Fig. 1), quite paradoxically it also occurs in the Philippines, but that needs to be checked with more new material. Potentially may reliably occur in other parts of Honshu and more southern main Japanese Islands. Remarks: Hantazuia kimotoi sp. nov. is externally similar to Hantazuia yugoikedai sp. nov., but reliably differs from it by the shape of its copulative stylet, which is significantly shorter and less curved (Fig. 8 I, J, N – P). The potential external difference between H. kimotoi sp. nov. and H. yugoikedai sp. nov. is that the latter has somewhat shorter anterior foot corners and is possibly larger in length at the adult stage (Fig. 8 B, C), but this needs to be checked further. Uncorrected COI p - distance within the Hantazuia kimotoi sp. nov. clade is 1.22 %. The COI uncorrected p - distances between the H. kimotoi sp. nov. clade and the H. yugoikedai sp. nov. clade are 12.3 % – 12.8 %, between the H. kimotoi sp. nov. clade and the H. imagawai sp. nov. clade they are 12.8 % – 13.1 %.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8CFFECFEABFF05FEA8FC29.taxon	description	(Figs 1, 2, 7 – 9) urn: lsid: zoobank. org: act: AFFA 946 E-E 27 D- 4 E 9 D-BDE 7 - 479 B 151608 D 3 Type species: Hantazuia yugoikedai sp. nov .. Diagnosis: Body narrow. Notal edge discontinuous. Cerata in separate indistinct partly scalloped small lobes or almost in short rows. Rhinophores smooth. Anterior foot corners present. Elaborate oral glands present. Anus preuroproctic. Edge of masticatory processes bears denticles that may form compound row of thickened denticles comprised of some smaller tubercles. Radula formula 0.1.0. Central teeth with non-compressed cusps and peculiarly arranged denticles, making tooth in total partially ‘ feather-like’. Lateral teeth absent. Proximal and distal receptaculum seminis. Moderately long vas deferens, and very distinct prostate. Penis conical with hollow stylet. Species included: Hantazuia yugoikedai sp. nov., Hantazuia kimotoi sp. nov., Hantazuia imagawai sp. nov., and? Hantazuia behrensi (Hermosillo and Valdes 2007) comb. nov. Remarks: See above under the diagnosis of the new family Hantazuidae fam. nov ..	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8CFFECFEFAFC5DFBBDF83A.taxon	description	(Figs 1, 7) urn: lsid: zoobank. org: act: D 4082 A 47 - 37 E 4 - 4437 - B 63 A- DAAD 04 D 77889 Etymology: In honour of citizen scientist Yugo Ikeda (池田雄 吾) who in the waters of Jogāshima Island (城ケ 島), Japan, observed nudibranchs for many years and made a very important contribution by collecting material for the present study. Holotype: KM 1044, L = 12 mm (live), north-western Pacific, Japan, Honshu, Jogāshima Island waters, stones, 10 – 20 m depth, 30 August 2023, coll. Yugo Ikeda. Paratype: KM 1070, L = 12 mm (live), north-western Pacific, Japan, Honshu, Jogāshima Island waters, stones, 10 – 20 m depth, 12 August 2023, coll. Yugo Ikeda. Paratype: KM 1071, L = 15 mm (live), north-western Pacific, Japan, Honshu, Jogāshima Island waters, stones, 10 – 20 m depth, 20 July 2023, coll. Yugo Ikeda. Description External morphology (Fig. 7 A – D, L, S) Body narrow. Foot and tail narrow, anterior foot corners moderate in length. Rhinophores similar in length to oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming up to about 20 – 25 small curved lobes with cerata in total (placed partly in a scallop-like pattern, if counting only the ceratal lobe-based groups, there will be correspondingly fewer in number) and separately placed cerata along dorsal edges, which are formed by a reduced discontinuous notal edge. Apices of cerata gradually pointed, with elongated cnidosacs. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below middle ceratal lobes. Reproductive openings lateral, below first-second and third-fifth ceratal lobes / separate cerata. Colour (Fig. 7 A – D, L, S) Background colour semi-transparent whitish to greyish. Cerata opaque yellowish to lemon-coloured (granulated when magnified) throughout most of the length with somewhat lighter bases. Cnidosacs in subapical parts of cerata darker yellowish-orange. Apical parts of cerata without opaque cap of white pigment, semi-transparent. Rhinophores covered with yellowish-whitish pigment over almost their entire length. The blackish ampulla, seminal receptacles, vas deferens and other ducts, as well as the lighter greyish (with darker elements inside) thick prostate, shine through the anterior part of the dorsal side and are characteristically well visible in living specimens (Fig. 7 A, D, L, S). Whitish gonad shines through the mid and posterior parts. Jaws (Fig. 7 G – I, P) Jaws oval-triangular. Edge of masticatory processes bears up to about 30 denticles that may form compound row of thickened denticles comprised of some smaller tubercles. Radula (Fig. 7 E, F, M, N, O) Radula formula in two specimens 17 – 18 × 0.1.0. Central teeth considerably narrow, elongate-triangular, rather feather-shaped with short, narrow, commonly double cusps. Central teeth bear up to at least 11 well-defined distinct, but denticles narrowly-arranged toward cusp. Lateral teeth absent. Reproductive system (Fig. 7 J, K, Q, R, T, U) Hermaphroditic duct leads to oval swollen ampulla. Vas deferens moderately long, narrow, somewhat convoluted, leads to very distinct, thick prostate. Penial sheath is oval. Penis is broadened conical, bears long, distinctly curved stylet with large oblique opening. Oviduct connects through insemination duct into female gland complex. Proximal receptaculum seminis elongate, moderately swollen. Distal receptaculum seminis present, rounded, almost sessile on a short stalk. Ecology: Shallow waters, stony habitats. Distribution: So far reliably known only from the Pacific side of middle Japan (Honshu). Potentially may occur in other parts of Honshu and more southern main Japanese Islands. Remarks: Hantazuia yugoikedai sp. nov. is externally similar to Hantazuia kimotoi sp. nov., but reliably differs from it by the shape of its copulative stylet, which is significantly longer and more curved (Fig. 7 J, K, Q, T). The potential external difference between H. yugoikedai sp. nov. and H. kimotoi sp. nov. is that the latter has potentially longer anterior foot corners and possibly is somewhat smaller in length at the adult stage (Fig. 7 B, D), but this needs to be checked further. Uncorrected COI p - distances within the Hantazuia yugoikedai sp. nov. clade are 0.3 % – 0.5 %. The COI uncorrected p - distances between the H. yugoikedai sp. nov. clade and the H. kimotoi sp. nov. clade are 12.3 % – 12.8 %, between the H. yugoikedai sp. nov. clade and the H. imagawai sp. nov. clade are 12.3 % – 12.8 %.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF89FFEBFC07FAD1FB12F849.taxon	description	(Figs 1, 2, 7 – 9; Table 4) urn: lsid: zoobank. org: act: 4 BC 82981 - 0061 - 412 A-ABA 0 - 329 FA 15 BCFDB Etymology: The new family Hantazuidae fam. nov. (stem is defined as ‘ Hantazu- ’) and new genus Hantazuia gen. nov. come from shorter variant of the Japanese katakana presentation ウミ ウシハンタ ーズ (transliterated as ‘ Umiushihantazu ’, or shortened to ‘ hantazu ’) of the English-based expression ‘ Umiushi hunters’, and ultimately as ‘ sea slug hunters’ (shortened to ‘ hunters’). This name has several layers of meaning, initially it is the name of a diving club in the waters of Jogāshima (城 ケ 島), specially devoted to observing nudibranchs in Japan, whose owner, Yugo Ikeda made very important contributions to collecting and observing members of the new family and genus for the present study. However, the much more general, world-wide and, therefore, universal meaning of the expression ‘ Umiushihantazu / hantazu — Umiushi hunters / hunters’ is that it is a metaphor of the growing community of citizen scientists, of posterior part of radula, SEM. O, radular teeth, details of posterior part of radula, SEM. P, jaw, SEM. Q, penis with strongly curved penial stylet, SEM. R, apical part of penial stylet, SEM. Paratype KM 1071 Honshu, Japan, 15 mm length (live). S, T: S, dorsal view. T, penis with strongly curved hollow penial stylet, SEM. U, scheme of reproductive system. Scale bars: E, 10 μm; F, 20 μm; G, 100 μm; H, 20 μm; I, 10 μm; J, 20 μm; K, 20 μm; M, 50 μm; N, 20 μm; O. 30 μm; P. 200 μm; Q. 100 μm; R. 10 μm; T. 100 μm; U, 0.5 mm. Photos and SEM images: Alexander Martynov. Abbreviations: a, ampulla; fgm, female gland mass; hd, hermaphroditic duct; p, penis; pr, prostate; psh, penial sheath; rsd, receptaculum seminis distal; rsp, receptaculum seminis proximal; st, penial stylet; vd, vas deferens. who in Japan, as well as in many other parts of the world, continue the painstaking and important work of observing and collecting nudibranch molluscs and other sea slugs to help scientists reveal and document the enormous diversity of these astonishing marine animals. Diagnosis: Body narrow. Notal edge discontinuous. Cerata in separate indistinct clusters on small lobes or in short rows, numerous per row. Rhinophores smooth. Anterior foot corners present. Anus pleuroproctic. Elaborate oral glands present. Edge of masticatory processes bears denticles that may form a compound row of thickened denticles comprised of some smaller tubercles. Radula formula 0.1.0. Central teeth with non-compressed cusps and peculiar denticles, making teeth in total partially ‘ feather-like’. Lateral teeth absent. Proximal and distal receptaculum seminis. Moderately long vas deferens, and distinct, thick prostate. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, conical with moderately long to a shorter hollow stylet. Genera included: Hantazuia gen. nov .. Remarks: Hantazuidae fam. nov. and Hantazuia gen. nov. are unique among all families of the superfamily Flabellinopsoidea so far known and sister to Flabellinoidea (Figs 1, 2; Tables 1 – 4) by the confirmed presence of a uniserial radula within the three new species of this new family (see Synopsis below). However, by molecular phylogenetic data Hantazuidae fam. nov. robustly aligns as sister to the morphologically very different triserial family Flabellinopsidae (Figs 1, 2). Furthermore, by combination of the long narrow body with discontinuous notal edge, uniserial radula, reproductive system without supplementary gland, and penis armed with a distinct stylet, Hantazuidae fam. nov. and Hantazuia gen. nov. are strongly different from both Flabellinopsoidea and Flabellinoidea and all taxa of the suborder Aeolidacea. The family ‘ Piseinotecidae’ (where an undescribed species of Hantazuidae fam. nov. and Hantazuia gen. nov. has been sometimes assigned as ‘ Piseinotecus ’ sp.; Gosliner et al. 2015) was recently revised and most of the included taxa have been transferred to the family Flabellinidae, but the presence of a uniserial radula had not been confirmed (Korshunova et al. 2017 a), continuing the need for a revision in the present study (see Synopsis above and below). However, morphologically, the type species of the genus Piseinotecus Er. Marcus, 1955 drastically differs from Hantazuidae fam. nov. and Hantazuia gen. nov. by a few clustered cerata, acleioproctic position of the anal opening, details of radular teeth, and an unarmed penis. For the type species of the genus Piseinotecus, P. divae Er. Marcus, 1955 (Marcus 1955), representing the only genus of the family Piseinotecidae Edmunds, 1970, molecular data are not available. However, even in the most complicated scenario, if after the molecular data become available, true Piseinotecus will align to a clade related to Hantazuia gen. nov., the significant morphological differences will warrant true Piseinotecus as a separate family, Piseinotecidae, from Hantazuidae fam. nov .. Remarkably, for only a few of the supposed former ‘ Piseinotecus ’ species for which the presence of the uniserial radula is confirmed, ‘ Piseinotecus ’ soussi Tamsouri et al., 2014, according to the data of the present study, in reality the species belongs to the family Unidentiidae as a new genus, placed in a completely different clade from the core Flabellinopsoidea and Flabellinoidea clades (Figs 1, 2; see description in Synopsis above). Additionally, a species ‘ Cuthona ’ behrensi has been described from the eastern tropical Pacific with external features (pleuroproctic anus) and patterns of a uniserial radula similar to Hantazuia gen. nov., but reported with an absence of cnidosacs and a supplementary gland inserted into the penis (Hermosillo and Valdes 2007). Molecular data are not available for ‘ Cuthona ’ behrensi. The presence of a supplementary gland, together with the other described characters, is unlikely and we consider this an error of description. Nevertheless, if further studies confirm its presence, that taxon will constitute a separate genus of the family Hantazuidae fam. nov., but currently we consider ‘ Cuthona ’ behrensi within the genus Hantazuia gen. nov. with a question mark. From all western warm-water and tropical Pacific species of the genus Hantazuia gen. nov. described below, the eastern Pacific ‘ Cuthona ’ behrensi differs by the details of its central radular teeth. This case further highlights the danger of the use of a pan-lumping approach, since the latter completely unrelated species has been masked using the erroneous catch-all ‘ Cuthona sensu latissimo ’. Thus, the ‘ family Piseinotecidae’ is undoubtedly highly polyphyletic and a uniserial radula clearly evolved several times within Aeolidacea (Figs 1, 2). In the present study we, therefore, for the first time take further significant steps in the reformation of the former highly artificial in many respects family ‘ Piseinotecidae’. Given the profound lumping and uncertain usage of the family ‘ Piseinotecidae’ and the genus ‘ Piseinotecus ’ throughout the history of nudibranch taxonomy, when former ‘ members’ of the family ‘ Piseinotecidae’ have been confirmed as belonging to at least three different and distantly related superfamilies Flabellinoidea, Flabellinopsoidea, and Unidentioidea (present study; Figs 1, 2), and to the three different families, namely, Flabellinidae, Hantazuidae fam. nov., and Unidentiidae, we did not include the family ‘ Piseinotecidae’ into the present Synopsis, and consider it as incertae sedis. See also the foundation of the aeolidacean superfamilies under remarks of another new family Chudidae fam. nov. above. The description and robust placement of the uniserial family Hantazuidae fam. nov. (including the descriptions of hidden diversity of no less than three species of the new genus Hantazuia gen. nov.) within an otherwise fundamentally triserial superfamily Flabellinopsoidea (Fig. 2) indeed represents a very remarkable and important result of the present study.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF0FF93FC24FDEBFEC2FF46.taxon	description	(Figs 1, 2, 13; Table 5) Thiele 1931: 453. Korshunova et al. 2017 a: 39. Type species: Himatella trophina Bergh, 1894. Diagnosis: Body wide. Notal edge present, continuous. Cerata in continuous rows. Rhinophores perfoliate. Anterior foot corners present. Central teeth almost pectinate, with moderately compressed apically narrow, basally distinctly widened cusp (in some posterior teeth the cusp can be reduced), and distinct, strong denticles. Lateral teeth denticulated with strongly attenuated process basally. Distal and proximal receptaculum seminis. Very short vas deferens expands into a broad penial sheath, prostate indistinct. Penis broad, discoid. Species included: Himatina trophina (Bergh, 1894) comb nov .. Detailed morphological data in Korshunova et al. (2017 a). Remarks: The genus Himatina was described more than 100 years ago, even without, at that time, the aid of molecular data, due to its immediate external and radular differences from any other coryphellid genera (Bergh 1894, Thiele 1931). The broad body of Himatina with its continuous notal edge represents an ancestral feature, more characteristic of the family Paracoryphellidae, than for the majority of Coryphellidae genera with their discontinuous or completely reduced notal edge. Perfoliate rhinophores are also very rarely present, especially in boreal Coryphellidae, being more characteristic of the families Flabellinidae and Facelinidae, and some warm-water coryphellids (see below). The radula of Himatina, with an almost pectinate general pattern, both central and lateral teeth strongly denticulated (the latter with a strongly attenuated process basally), is significantly different from all Coryphellidae, and by its general pattern more similar to the phylogenetically distantly related genus Polaria from the family Paracoryphellidae (Korshunova et al. 2017 a), than to any other true coryphellid genera. In total, the genus Himatina is different from any known genera of the family Coryphellidae by the combination of a wide body, perfoliate rhinophores, almost pectinate central teeth, and a very short vas deferens. Comparison of the genus Himatina with all valid, currently included Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF3FF93FC4CFDEBFA98F82A.taxon	description	(Figs 1, 2, 13; Table 5) Korshunova et al. 2017 a: 39 – 40. Type species: Coryphella falklandica Eliot, 1907. Diagnosis: Bodymoderatelywide. Notaledgepresent, continuous. Cerata in continuous rows. Rhinophores wrinkled. Anterior foot corners present. Central teeth with non-compressed wide cusp and distinct denticles. Lateral teeth denticulated without attenuated process basally. Receptaculum seminis not evident. Vas deferens very short, expands into a broad penial sheath, prostate indistinct. Penis broad, lobe-shaped. Species included: Itaxia falklandica (Eliot, 1907) comb. nov .. Detailed morphological data in Korshunova et al. (2017 a). Remarks: The genus Itaxia inhabits exclusively the southern parts of South America and possibly some more distant localities in the Southern Ocean (which may represent, in turn, as yet undetected hidden diversity of Itaxia; Odhner 1944, Marcus 1959). According to the molecular phylogenetic data of all the phylogenetic analyses performed so far (Korshunova et al. 2017 a, present study; Figs 1, 13), it is the basal-most coryphellid taxon. Morphologically the characters of Itaxia rather mosaically combine the ancestral continuous notal edge, but at the same time presents an extremely reduced vas deferens and also possesses a very strong cusp of the central teeth (Korshunova et al. 2017 a). Thus, Itaxia therefore very well demonstrates multilevel fine-scale diversity in its morphology and molecular phylogenetic data. The genus Itaxia was named after the word itax meaning ‘ south’ in the currently extinct Yagán language from the southern tip of South America [but in 2017, when the Korshunova et al. (2017 a) monograph with the name Itaxia was published, the last native Yagán speaker was still alive], to respect these indigenous southernmost people in the world and their ancestral heritage. Likewise the genus Itaxia represents one of earliest offshoots of the basal radiation of the family Coryphellidae (Figs 1, 13) and keeps some of the ancestral features of the common ancestor of all Coryphellidae. Comparison of the genus Itaxia with all valid, currentlyincluded Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF80FFE2FC6CFA83FADAF83E.taxon	description	(Figs 1, 10) Mgueolia almamater Korshunova, Fletcher, Martynov gen. et sp. nov.: Martynov and Korshunova 2025: 27 – 8, figs F 1, F 2. urn: lsid: zoobank. org: act: 07842 F 2 C-EF 32 - 4 D 96 - 80 BB- 050 D 44 EA 5 C 17 Holotype: KM 980, L = 19 mm (live), north-western Pacific, Russia, Kurile Islands, Urup Island, stones, 30 – 40 m depth, 1 September 2022, coll. T. A. Korshunova and A. V. Martynov. Paratype: KM 885, L = 24 mm (live), north-western Pacific, Russia, Kurile Islands, Urup Island, stones, 30 – 40 m depth, 27 August 2021, coll. T. A. Korshunova and A. V. Martynov. Paratype: KM 1007, L = 30 mm (live), north-western Pacific, Russia, Kurile Islands, Urup Island, stones, 30 – 40 m depth, 21 August 2022, coll. T. A. Korshunova and A. V. Martynov. Etymology: See above under the genus name. M, radular teeth, details of posterior part of radula, SEM. N, radular teeth, details of posterior part of radula, SEM. O, radular teeth, details of central posterior tooth, SEM. P, radular teeth, details of lateral posterior tooth, SEM. Q, jaw. R, details of masticatory process of jaw, SEM. S, details of masticatory process of jaw, SEM. T, scheme of reproductive system. Scale bars: K, 300 μm; L, 300 μm; M, 30 μm; N, 30 μm; O, 10 μm; P, 10 μm; Q, 300 μm; R, 30 μm; S. 10 μm; T 0.5 mm. Photos: Tatiana Korshunova. SEM images: Alexander Martynov. Abbreviations: a, ampulla; fgm, female gland mass; hd, hermaphroditic duct; p, penis; pvd, prostatic vas deferens; psh, penial sheath; rsd, receptaculum seminis distal; rsp, receptaculum seminis proximal. Description External morphology (Fig. 10 A – J) Body moderately wide. Foot moderately wide, anteriorly oblique with short foot corners. Rhinophores somewhat shorter or similar in size to oral tentacles, peculiarly wrinkled to smooth. Dorsal cerata relatively short, partly elongate, commonly conspicuously swollen, continuously attached to well-defined uninterrupted notal edge without forming clusters. Notal edge narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of cerata. Anal opening on right side below notal edge close to middle body part, difficult to observe even in living specimens. Reproductive openings on right side. Tail short and pointed, extending only a short distance beyond last cerata. Colour (Fig. 10 A – J) Background colour whitish with sometimes a little pinkish shadow. Digestive gland diverticula with various shades of reddish-pink, reddish-brown, or salmon coloration. Rhinophores are similar in colour, but somewhat lighter. Oral tentacles whitish to pinkish. Ceratal apices more orange, with shine through whitish cnidosacs. Foot whitish with a little pinkish hue. Pinkish gonad partly shines through the ventral side of the foot. Jaws (Fig. 10 Q – S) Jaws oval. Edge of masticatory processes bears up to about 40 or more denticles that may form up to at least eight longitudinal rows of denticles and tubercles from the internal side, diminishing toward the inner part of the jaw. Denticles at the very edge of masticatory processes considerably elongated, narrowing toward the apical parts. Radula (Fig. 10 K – P) Radula formula 32 × 1.1.1. General pattern of radula remarkably similar to family Eubranchidae, with narrow cusp of central teeth significantly compressed by adjacent lateral denticles and almost smooth to slightly denticulated lateral teeth with strong broad ventro-lateral bases. Up to at least seven distinct lateral denticles on central teeth. Lateral teeth smooth to slightly denticulated with at least up to five slight serrations / reduced denticles on some teeth. Reproductive system (Fig. 10 T) Hermaphroditic duct leads to moderately long, thick, convoluted ampulla of few whorls. Vas deferens long, relatively narrow, no distinct prostate. Penial sheath elongated. Penis elongated conical. Oviduct connects through insemination duct into female gland complex. Both distal and proximal receptaculum seminis detected, somewhat rounded, similar in size, almost sessile, on very short stalks. Ecology: Shallow water, upper subtidal, stony environment. Distribution: So far discovered only at the Urup Island, Kurile Island, in NW Pacific. Remarks: Hereindetaileddescriptionandmoleculardata (Figs 1, 2, 10) are for the first time provided. All three Mgueolia almamater formed a maximally supported clade (PP = 1, BS = 100) within the family Paracoryphellidae clade. Uncorrected COI p - distance within the M. almamater clade is 0 – 0.3 %. The COI minimal uncorrected p - distance of 12.7 % was found between the M. almamater clade and Ziminella salmonacea. For more see above under the genus name.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF80FFE2FC6CFA83FADAF83E.taxon	description	Subfam. Flabellininae Bergh 1889: 215. ‘ Genus Flabellina sensu latissimo ’ Gosliner and Griffiths 1981: 105, 109 – 15.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF80FFE2FC6CFA83FADAF83E.taxon	diagnosis	Diagnosis: Body moderately narrow. Notal edge discontinuous or completely reduced. Cerata in separate clusters, on elevations or distinct stalks. Rhinophores smooth, annulate, or papillate. Anus mixed (pleuroproctic in higher acleioproctic position) or pleuroproctic. Elaborate oral glands present, commonly penetrate below anterior cerata. Masticatory edges of jaws with several rows of compound, sharpened or tubercle-like denticles. Radula formula 1.1.1. Central teeth usually with compressed cusp by adjacent lateral denticles. Lateral teeth with attenuated process basally, usually denticulated, rarely smooth. Number and position of receptaculum seminis variable: two separate ones, or double proximal and single distal, or double distal one, in few cases a proximal receptaculum is not evident. Vas deferens usually long, with indistinct prostate, more rarely short. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, usually elongated conical, narrow, unarmed. Genera included: Calmella Eliot, 1910, Carronella Korshunova et al., 2017, Coryphellina O’Donoghue, 1929, Edmundsella Korshunova et al., 2017, Flabellina Gray, 1833 in Griffith and Pidgeon, 1833 – 34, and Paraflabellina Korshunova et al., 2017. Remarks: The family Flabellinidae proper, after moving morphologically and molecularly highly heterogenous diversity into at least six separate families (Korshunova et al. 2017 a, present study) placed in four different distantly related superfamilies Samloidea, Apataoidea, Flabellinopsoidea, and Flabellinoidea (Figs 1, 2) represents a well-diagnosed fine-scale taxonomic unit, externally characterized by notal edge usually modified into some low stalk- or elevation-like clusters (genera Carronella, Coryphellina, and Calmella) or into some very distinct, high stalks as in the proper genus Flabellina. Internally, the taxa of the family Flabellinidae commonly possess a compressed cusp of the central teeth and a long to moderate vas deferens, but not commonly as short as in the family Coryphellidae.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF80FFE0FF00FCAFFBEFFB67.taxon	description	(Figs 1, 10) urn: lsid: zoobank. org: act: 03 CFDFB 2 - 0 F 06 - 4716 - 9494 - B 85 EAC 50 E 0 C 6 Type species: Mgueolia almamater Korshunova et al., 2025 Etymology: In honour of the first, largest and the most famous Russian University, Moscow State Univesity (MGU, Moskovskyi Gosudarstvennyi Universitet in Russian), and its 270 - year anniversary in 2025. Additionally, ‘ Aeolia’ (short form ‘ Eolia’) both refers to aeolidacean nudibranchs and also means a floating island in Greek mythology. ‘ Aeolus’ Kingdom can be metaphorically assigned to Moscow State University as a dynamic ‘ island’, permanently searching for knowledge and education in an ocean of the world / universe that still needs to be understood. Ultimately, the combination of genus and species name Mgueolia almamater (Alma mater = nourishing mother) refers to both a common symbolic word for any worldwide university to denote a cradle of education, and in reference to the obviously relict nature of the new species and thus its ‘ alma mater’ is the middle Kuril Islands, where probably that externally splendid and internally amazing taxon was able to survive. Diagnosis: Body moderately wide. Notal edge present, continuous. Cerata not stalked, continuous. Rhinophores smooth to wrinkled with some peculiar folds, somewhat shorter or similar in size to oral tentacles. Anterior foot corners present, short. Anus pleuroproctic under the notal edge, but external opening is very difficult to observe both in living and preserved specimens due to the tight adherence of the notal edge with cerata to the body sides. Edges of masticatory processes bear denticles that may form several longitudinal rows of denticles and tubercles from the internal side, diminishing toward the inner part of the jaw. Central teeth with narrow, compressed cusp, the majority of lateral denticles clearly delineated from cusp. Lateral teeth smooth to very weakly serrated / wavy with a long, broad process latero-basally, not significantly smaller than central teeth. Both distal and proximal receptaculum seminis present. Vas deferens long, coiled with several loops, relatively narrow, no distinct prostate. Massive external penial collar absent. Penis elongated conical, unarmed. Species included: Mgueolia almamater Korshunova et al., 2025 (Mgueolia almamater Korshunova et al. gen. et sp. nov. in Martynov and Korshunova 2025). Remarks: Mgueolia almamater Korshunova et al., 2025, herein for the first time described in detail, according to the molecular phylogenetic data, is robustly placed as a distinct clade of the family Paracoryphellidae, sister to all the genera so far known — Chlamylla, Paracoryphella, and Polaria (Figs 1, 2) — with external features generally in agreement with all genera of the family Paracoryphellidae (a continuous notal edge and numerous cerata in continuous rows (Fig. 10 A, B, D – I )). However, according to the radular patterns, the new genus is drastically different from all known adult paracoryphellids by the combination of a narrow, compressed cusp of the central tooth and almost smooth lateral teeth with a broad massive latero-basal process (Fig. 10 P), similar to the family Eubranchidae from the completely different and phylogenetically very distantly related superfamily Fionoidea (Figs 1, 2). The somewhat swollen cerata of the new genus and species also partly recall members of the family Eubranchidae. Thus, Mgueolia almamater is a highly unusual and remarkable taxon, that evolution preserved in the rarely visited and understudied waters of the middle Kurile Islands, and combined both relatively advanced and very archaic features. The discovery and description of Mgueolia almamater represents an important landmark in nudibranch taxonomy.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF2FF94FF4BFF1AFE52FEE2.taxon	description	(Figs 1, 2, 13, 17; Table 5) Korshunova et al. 2017 a: 40. Type species: Eolis gracilis Alder and Hancock, 1844. Diagnosis: Body moderately narrow. Notal edge present, discontinuous. Cerata in several groups. Rhinophores smooth. Anterior foot corners present. Central teeth rather square in shape with narrow to moderately wide cusp and distinct denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Very long, convoluted vas deferens expands into a narrow penial sheath, prostate indistinct. Penis narrow, conical. Species included: Microchlamylla gracilis gracilis (Alder and Hancock, 1844) comb. nov., Microchlamylla gracilis zfi Korshunova et al., 2017 comb. nov., and Microchlamylla amabilis (Hirano and Kuzirian, 1991) comb. nov. Detailed morphological data in Korshunova et al. (2017 a). Remarks: The genus Microchlamylla is particularly unique among the family Coryphellidae in possessing a very long, coiled vas deferens (Fig. 17). This feature is rather characteristic of the different basally placed family, Paracoryphellidae, and the basal-most to Flabellinoidea family, Flabellinopsidae (Figs 1, 2) and cannot in any way be considered merely part of ‘ natural variability’ (Ekimova et al. 2022). In living adult specimens, several loops of the vas deferens even shine through the anterior part of the dorsal side; this, in combination with a discontinuous notal edge, makes the genus Microchlamylla immediately recognizable. Further, the reproductive system of Microchlamylla gracilis gracilis and M. amabilis differs in the details of the proportions of the seminal receptacles, as well as the details of the coiling of the vas deferens (Fig. 17 A, B), but this needs to be addressed further. Remarkably, the valid subspecies Microchlamylla gracilis zfi from the high Arctic instead differs from both the North Atlantic boreal M. gracilis gracilis and the North Pacific M. amabilis by having a considerably wider vas deferens (Korshunova et al. 2017 a). The relatively square shape of the central radular teeth of the genus Microchlamylla is also distinct from the central teeth shape in a majority of the genera of the family Coryphellidae (Hirano and Kuzirian 1991, Korshunova et al. 2017 a). In the molecular phylogenetic analysis, the genus Microchlamylla invariably forms a distinct maximally supported clade (PP = 1, BS = 100), which is placed basally to a majority of the coryphellid genera (Figs 1, 2, 13), and together with genus Itaxia represents relics of early coryphellid evolutionary radiation. Twelve Microchlamylla gracilis formed a separate highly-supported clade (PP = 1, BS = 91), but 10 M. amabilis (Fig. 13) branched directly from the clade. Uncorrected COI p - distances between the 10 M. amabilis are 0.4 % – 2.0 %, between the 12 M. gracilis are 0.2 % – 1.6 %. Uncorrected COI p - distances between M. amabilis and M. gracilis are 3.8 % – 6.1 %. There are analyses and a discussion of Microchlamylla gracilis and M. amabilis in Ekimova et al. (2022), where conflicting information on the taxonomy M. gracilis and M. amabilis is provided (Supporting Information, Fig. S 2). Microchlamylla amabilis is defined as a combination of Microchlamylla amabilis, Coryphella amabilis, and Coryphella gracilis. Completely opposite conclusions are presented in the Discussion and in the Abstract: ‘ We suggest treating M. gracilis and M. amabilis as two separated allopatric species’ and ‘ for Microchlamylla gracilis and M. amabilis, their synonymization under the name M. gracilis is suggested’. Reproductive systems of two ‘ Coryphella ’ gracilis are presented in Ekimova et al. (2022: fig. 8 E, F) according to the caption under figure 8, but in the Discussion, figure 8 E, F is used to illustrate the reproductive systems of ‘ Borealea nobilis and B. sanamyanae ’ noting that ‘ the reproductive system was found to be similar in these two species (Ekimova et al. 2022: fig. 8 E, F) ’. Microchlamylla gracilis and M. amabilis were reasonably indicated as two separate species in Korshunova et al. (2017 a) and in the present study additional data is provided. Comparison of the genus Microchllamylla with all valid, currently included Coryphellidae genera is presented in Table 5. In this respect the case of the family Coryphellidae is again particularly relevant for the most general understanding of how to maximally coherently represent the evolutionary-derived biological diversity in a system of apparently ‘ static’ taxonomic names, an ultimate goal of any systematic study even in the current profoundly ‘ phylogenetic era’. Because if all the coryphellid diversity were lumped into the single genus ‘ Coryphella ’, then, for example, the genus Microchlamylla — a genus that, according to the molecular phylogenetic data (Figs 1, 2, 13), is very distant from the true Coryphella, and shows the presence of a very long vas deferens in the reproductive system (Fig. 17), which is more characteristic of the completely different molecular clade of the family Paracoryphellidae (Korshunova et al. 2017 a, present study, Synopsis; Figs 1, 2, 10) — disappears. Thus, if Microchlamylla were lumped into the genus Coryphella, then not only that particular genus would be dismissed, but also the entire superfamily Flabellinoidea in all its large-scale and fine-scale diversity (Figs 1, 2, 5, 13; Tables 1 – 4). All three currently recognized valid taxa of the genus Microchlamylla, including M. gracilis gracilis, M. gracilis zfi, and M. amabilis, show distinct phylogeographic patterns in their distribution (Fig. 17 C). Microchlamylla gracilis gracilis inhabits boreal waters with some cold-water influence on both sides of the North Atlantic, including the Barents Sea, M. gracilis zfi inhabits the high Arctic latitudes at least at Franz Joseph Land (Korshunova et al. 2017 a, present study; Fig. 17 C), whereas M. amabilis is distributed in the North Pacific on both western and eastern coasts with no known overlap in the Arctic (Fig. 17 C). Occidenthella Korshunova et al., 2017, reinstated (Figs 1, 2, 13; Table 5) Korshunova et al. 2017 a: 42 – 3. Korshunova et al. 2017 b: 140. Type species: Coryphella athadona Bergh, 1875. Diagnosis: Body narrow. Notal edge almost completely reduced. Cerata in several groups. Rhinophores smooth. Anterior foot corners absent. Central teeth with non-compressed moderately wide cusp and distinct denticles. Lateral teeth denticulated with moderately attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens very short, expands into a broad penial sheath with a very distinct, strongly protruding accessory gland external to penis. Penis small, amorphous. Species included: Occidenthella athadona (Bergh, 1875) comb. nov .. Detailed morphological data in Korshunova et al. (2017 a). Remarks: The genus Occidenthella Korshunova et al., 2017 is one of the most aberrant genera not only within the family Coryphellidae, but within almost all taxa of the superfamily Flabellinoidea. The genus Occidenthella is different from an absolute majority of triserial aeolids by the complete reduction of anterior foot corners (Bergh 1875, Baba 1987 a, Korshunova et al. 2017 a), a feature common for the different, distantly related superfamily Fionoidea (Figs 1, 2), but not for Flabellinoidea (see the Synopsis of all the Aeolidacean families and consideration of the aeolidacean superfamilies under Remarks to a new family Chudidae above), and the presence of a very distinct accessory gland (Korshunova et al. 2017 a), which is also partly similar to the supplementary gland of Cuthonidae, Trinchesiidae, Eubranchidae, and other fionoidean families (but definitely independent in its origin, see molecular phylogenetic tree; Figs 1, 2; Tables 3, 4). Externally, Occidenthella is commonly a very narrow coryphellid (even with all the reservation about the relativity of the terms ‘ narrow’ and ‘ wide’) with almost a completely reduced notal edge (in this case, the last remnants of the notal edge are possible to distinguish mostly at anterior ceratal clusters only after careful examination under a stereomicroscope or in macro photographs), which in combination with significant differences in its internal morphology, makes this genus immediately recognizable. This example is especially relevant for the confirmation of the importance and validity of the multilevel fine-scale diversity methodology, because according to the molecular data, the genus Occidenthella is a sister-genus to Orienthella (Figs 1, 13), which is fundamentally different both externally and internally from Occidenthella (Korshunova et al. 2017 a). Thus, the significant morphological differences, comparable with family-level differences, may arise phylogenetically relatively fast, but this does not mean that we should lump all that diversity into a single genus. This would be a truly anti-evolutionary action, because, obviously, evolution is not merely a genetic divergence, but a complex ontogeny-based process, which includes both genetic and epigenetic elements (Martynov and Korshunova 2022). Clade Occidenthella has the closest sister-position to the clade Orienthella (Korshunova et al. 2017 a, b, present study; Figs 1, 13). Comparison of the genus Occidenthella with all valid, currently included Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA7FFC6FC75F8B0FAD6FF66.taxon	description	(Figs 1, 2; Table 4) Korshunova et al. 2017 a: 2, 71, 73 – 8, supplementary materials. Diagnosis: Body wide, massive. Notal edge present, continuous, reduced. Cerata non-elevated, very numerous per row. Ceratal rows branched. Rhinophores wrinkled. Special wedge-shaped structure between rhinophores. Anus cleioproctic, placed clearly toward posterior part of body, uniquely among member of the superfamily Fionoidea, or very rarely pleuroproctic. Masticatory edges of jaws commonly bear single row of simple or compound, sharpened denticles. Radula formula 0.1.0. Central teeth usually with strong cusp, not compressed by adjacent lateral denticles. Proximal receptaculum seminis. Vas deferens moderately long, prostate indistinct. Supplementary gland present, inserts into penis. Massive external permanent penial collar absent. Penis internal, broad, unarmed. Genera included: Murmania Martynov, 2006 and? Guyvalvoria Vayssière, 1906. Remarks: Although it possesses a uniserial radula, the family Murmaniidae otherwise displays other unique, clearly ancestrally fuelled sets of characters for the superfamily Fionoidea (Fig. 2), but compared to the triserial Eubranchidae, the distinctions are at the level of external morphology (see: Martynov et al. 2020). Particularly, the family Murmaniidae has a distinctly large, wide body [such massive body patterns are not very common within the suborder Aeolidacea, and can be assigned mostly to a few representatives of the superfamilies Flabellinoidea (family Paracoryphellidae, genus Chlamylla), Aeolidioidea (family Aeolidiidae, genus Aeolidia) and also contains only single new family Chudidae fam. nov. superfamily Chudoidea superfam. nov., see Synopsis below]. Murmaniidae have a rudimentary notal edge, a definite ancestral feature that is common within the superfamily Flabellinoidea, in turn rare in the superfamily Aeolidioidea, but within the superfamily Fionoidea, the family Murmaniidae is the only benthic family with such a character. Furthermore, the anus of Murmaniidae is distinctly cleioproctic, a character state that is rare within the predominantly acleioproctic superfamily Fionoidea. The conclusion in Kim et al. (2024) that the cleioproctic anus of Murmaniidae, and other Fionoidea families, principally differs from the cleioproctic anus of Facelinidae is erroneous. Moreover, the placement of the anus toward the posterior part of the dorsal side, and even one instance of pleuroproctic anal position (Martynov 2006 a), further highlights the uniqueness of the family Murmaniidae. At the same time, the reproductive system of Murmaniidae shows insertion of a supplementary gland into the penis, common for a majority of the families, and not into the vas deferens, as it does, for example, within the family Cuthonellidae (see Synopsis below). Taking into consideration that the insertion of a supplementary gland into the vas deferens is also so far only confirmed for the restricted, true genus Eubranchus (with types species E. tricolor) from the family Eubranchidae, and from the drastically different family, Calmidae (see below), and both are distantly related to Murmaniidae (Figs 1, 2), therefore, insertion of a supplementary gland into the vas deferens appears as an ancestral character for the superfamily Fionoidea. Thus, as real evolutionary patterns commonly generate significant mosaicism in the ‘ resulting’ taxa regarding ancestral and unique or other ‘ novel’ characters (Figs 1, 2; Synopsis), any lumping or putative ‘ intermediate character approach’ at any level, from order to ‘ species’, will fundamentally produce the wrong picture of the underlying evolutionary pathways in the level of taxonomic presentation, compared to fine-scale differentiated taxonomy (Synopsis; Figs 1, 2; Tables 1 – 4).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF97FFF6FC35FCECFD16FC77.taxon	description	(Figs 1, 2; Table 4) Bergh 1905: 226. Martynov et al. 2019: 90, 111 – 2. Diagnosis: Body moderately broad to narrow. Notal edge completely reduced. Cerata in arches or rows, numerous per row. Rhinophores smooth, with swellings or perfoliate. Cleioproctic anus. Masticatory edges of jaws moderately to very strongly denticulated, denticles relatively simple to compound. Radula formula 0.1.0. Central teeth with distinct denticles, sometimes reduced, cusp non-compressed or compressed. Proximal receptaculum seminis. Vas deferens from very long to short, prostate indistinct or distinct. Accessory gland present in some taxa. Massive external permanent penial collar absent. Penis internal, conical, sometimes with internal glands, or massive, papillated, unarmed or armed with stylet. Genera included: Dondice Er. Marcus, 1958, Godiva Macnae, 1954, Hermissenda Bergh, 1879, Nanuca Er. Marcus, 1957, Nemesignis Furfaro and Mariottini, 2021, and Phyllodesmium Ehrenberg, 1831. Remarks: The family Myrrhinidae Bergh, 1905 highlights the paradoxical ‘ nature’ of contemporary taxonomy, when at the morphological level the family Myrrhinidae, even though it comprises a relatively few number of genera, represent a heterogenous assemblage, but because it was uncovered as paraphyletic compared to the other Facelinidae, its separation (Martynov et al. 2019) was immediately accepted and did not promote any notable discussion. While we apparently must be satisfied that such a case is ‘ allowed’ to exist, it, in reality, clearly reveals the fundamental problem of modern taxonomy, which predominantly relies on the results of molecular phylogenetic analysis without a deep understanding of basic biological facts: that every taxon does not represent merely a branch from the ‘ endless phylogenetic tree’, but inevitably is comprised of individual organisms, each in all its ontogenetic complexity, and only these complex individuals interact on one side to make a permanent ‘ evolutionary flow’, but on the other side always remain individuals, not merely a part of a human-constructed ‘ phylogenetic tree’ (see also: Martynov and Korshunova 2022). That is why the more taxonomy is differentiated, the more it departs from overformalized phylogenetic trees and approaches the true element of any evolutionary process — a dynamic individual with a particular set of characters. A further paradox is that the family Myrrhinidae was uncovered as phylogenetically more related to the family Aeolidiidae than to the rest of Facelinidae, whereas at the morphological level Myrrhinidae is similar to Facelinidae, and not to Aeolidiidae. Therefore, it is perfectly possible in a case when morphologically similar families are mosaically distributed within the superfamily Aeolidioidea using that logic of ‘ intermediate morphology’ during pan-synonymization events in another aeolidacean superfamily Flabellinoidea (Gosliner and Griffiths 1981), to lump the family-level diversity of the aeolidioidean superfamily into merely one family, Aeolidiidae / Glaucidae, just because of molecular phylogenetic data (Figs 1, 2). However, the potential synonymy of fine-scale differentiated families, Myrrhinidae and Aeolidiidae, is not discussed, whereas, again, fundamentally similar cases at different levels of the superfamilies Fionoidea and Flabellinoidea are instead the target of highly dismissive synonymy without any morphological basis.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB2FFD7FCBBFCDAFAB1FEA1.taxon	description	(Fig. 2; Tables 1 – 3) = Proteolidoidea Odhner in Franc 1968: 881. Diagnosis: Unique within the Aeolidacea superfamily in having an oligoserial radula, with the number of rows of lateral teeth more than one and less than 10. Notal edge present, continuous to discontinuous. Cerata are not placed in regular rows, on lateral notal extensions. Rhinophores with folds and wrinkles. Anus pleuroproctic. Nephroproct in front of genital openings reported as another unique feature. Anterior foot corners present, partly fused with thickened anterior edge of foot. No elaborate oral glands. Masticatory edges of jaws smooth. Central teeth with short basis and strong cusp, not compressed by adjacent lateral denticles. Lateral teeth denticulated, placed in more than one longitudinal row on each side of the central teeth. Distal seminal receptaculum. Clasping organ in female part of reproductive system absent. Vas deferens commonly very long, prostate indistinct. Supplementary gland in male part of reproductive system or other accessory glands absent. Massive external permanent penial collar present or absent. Penis unarmed, external, attached directly to the body wall in a single species ‘ Notaeolidia ’ schmekelae Wägele, 1990 or internal, broad and unarmed in two other currently recognized Notaeolidia species. Families included: Notaeolidiidae Eliot, 1910.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB2FFD7FCBBFCDAFAB1FEA1.taxon	diagnosis	Diagnosis: Body wide. Notal edge reduced, continuous to discontinuous. Cerata on lateral extensions, numerous per row. Ceratal rows branched. Rhinophores with folds and wrinkles. Anus pleuroproctic under notal edge. Masticatory edges of jaws smooth. Radula formula 7 - 2.1.2 - 7. Central teeth with short basis and strong cusp, not compressed by adjacent lateral denticles. Lateral teeth denticulated, basal part more commonly is not considerably elongated, but can be also widened. Distal receptaculum seminis. Vas deferens commonly very long, prostate indistinct. Supplementary and accessory glands absent. Massive external permanent penial collar present or absent. Penis external or internal, broad, unarmed. Genera included: Notaeolidia Eliot, 1905, at least for ‘ Notaeolidia ’ schmekelae Wägele, 1990, needs to be further established a separate genus, because of the presence of a non-retractable penis, which is directly attached to the body wall (combined with the massive external penial collar), and presence of the widened basal part of the lateral teeth (Table 4). Remarks: Although molecular data for the family Notaeolidiidae have been known previously (e. g. Goodheart et al. 2018), in the present study, for the first time, the molecular phylogenetic data for Notaeolidiidae have been integrated with all known families of the suborder Aeolidacea in a comprehensive, all-encompassing phylogeny (Figs 1, 2). According to the present analysis, the family Notaeolidiidae, placed together with the superfamilies Samloidea and Apataoidea, is sister to all other aeolidacean superfamilies and families (Figs 1, 2). This position is well corroborated by morphological data, since superfamily Notaeolidioidea and family Notaeolidiidae are the only taxa within the whole suborder Aeolidacea that have preserved an ancestral oligoserial radula (Odhner 1934, Wägele 1990) (Fig. 1). The sister-position of the oligoserial superfamily Notaeolidioidea to the triserial superfamily Samloidea well highlights the direction of the consequent reduction of the ancestral oligoserial radula, first to the triserial radula in several superfamilies of the Aeolidacea [Samloidea, Apataoidea, Fionoidea (family Eubranchidae only), Chudoidea superfam. nov, Cumanotoidea, and Flabellinoidea], and then, reduced into a uniserial radula, at least four times independently, within the superfamilies Unidentioidea (only the single included family Unidentiidae), Fionoidea (the absolute majority of families), Aeolidioidea, and Flabellinopsoidea (only the new family Hantazuidae fam. nov. is confirmed as having a uniserial radula, see Synopsis below; Fig. 2). Superfamily Samloidea Korshunova et al., 2017, herein established	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB2FFD7FCBBFCDAFAB1FEA1.taxon	description	(Fig. 2; Tables 1 – 3) Diagnosis: Aeolidacean superfamily with triserial radula. Notal edge discontinuous or completely reduced. Cerata on low elevations. Ceratal rows branched. Rhinophores perfoliate. Anus pleuroproctic under the reduced notal edge or shifted toward the acleioproctic position. Anterior foot corners present. Elaborate oral glands present. Jaws with masticatory edges bear a single to several moderate or strong denticles. Central teeth usually with strong cusp, rarely compressed by adjacent lateral denticles. Lateral teeth denticulated. Distal and proximal receptaculum seminis or only a proximal receptaculum. Clasping organ in female part of reproductive system absent. Vas deferens usually short, to moderate, prostate indistinct or distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, not considerably widened, unarmed. Families included: Samlidae Korshunova et al. 2017.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFBAFFD2FCA5FDB5FADCFCAE.taxon	diagnosis	Diagnosis: Notum primarily present, often reduced. Shell in adult state absent. Rhinophores primarily separated, secondarily united, initially rhinophores connected to broad oral veil that replaces anterior notum, often reduced, or oral tentacles formed. True gill absent, often various secondary structures (branched outgrowths, cerata, etc.) arranged latero-dorsally on both sides of the body. Anal opening initially remains in ventro-lateral position, secondarily may shift dorsally. Jaws entire, radula initially multiserial, with hooked teeth, often reduced to one tooth per row, central teeth usually present. Digestive gland initially entire, usually branched to varying degrees, in many taxa branches penetrate dorsal processes. Reproductive system usually considered to be diaulic, but triaulic also present. Suborders included: (See Remarks below for details) suborder Arminacea Odhner, 1934, restricted, reinstated; suborder Tritoniacea Lamarck, 1809, reinstated; suborder Dendronotacea Odhner, 1934, restricted, reinstated; suborder Janolacea Minichev and Starobogatov, 1979, amended, reinstated; suborder Aeolidacea Odhner, 1934, reinstated. Remarks: To reinstate the suborder status for the Aeolidacea, first the higher order-level systematics of ‘ nudibranchs’, which has an intricate history, needs to be clarified. Initially, the separate order Nudibranchia was for the first time introduced in the same work of Blainville (1814) on the same page, but under two different names — Polybranches (Blainville 1814: 177, not to be confused with the subsequent misapplication for sacoglossans), and Nudibranches (Cuvier inBlainville 1814: 177). The original diagnosis for Blainville’s order Polybranchia clearly reads ‘ respiratory processes subdivided into numerous small branches’, and further, importantly, placed ‘ at two sides of the whole body’ as ‘ a main distinguishing character’. Simultaneously, for dorids Blainville (1814: 178) introduced the separate order Cyclobranches (not to be confused with the subsequent misapplication of the name ‘ Cyclobranches’ for patellids and chitons by Cuvier 1817: 451). Dorids immediately differ from ‘ Nudibranchia’ by the presence of the predominantly dorsal gill, modified into a circle, at least in part homological to the lateral gill of the order Pleurobranchida (Wägele and Willan 2000), by ontogenetic patterns (Martynov 2011, Martynov and Korshunova 2015, Martynov et al. 2022), and, regardless of its sister-position to Nudibranchia, forms a robustly supported, separate clade, according to the molecular phylogenetic analyses (Korshunova et al. 2020 a, Knutson 2021). Evidently, under the name Cyclobranches (Cyclobranchia), Blainville implied precisely the circular gill of dorids, whereas included the ‘ addition’, onchidiids, possess different secondary dorsal respiratory structures. Unfortunately, the proposal by Blainville, which is strongly supported by modern multisource data, has been historically diminished under the sweeping name ‘ Nudibranchia’ (Cuvier in Blainville 1814: 177, Cuvier 1817: 389), although the ordinal status for dorids has been persistently attempted to be resurrected under several different names (Wägele and Willan 2000). Thus, despite the fundamental differences between Nudibranchia and Doridida, explicitly indicated at the ordinal ranks very early in the history of sea slug classification, currently dorids are considered just a ‘ suborder’ of ‘ Nudibranchia’ s. l., whereas Nudibranchia in the original sense was renamed significantly later as ‘ Cladobranchia Willan and Morton, 1984 ’ (Wägele and Willan 2000). Importantly, in Blainville (1814: 177, our italics), it is unequivocally stated that ‘ Mr. de Blainville gives the fourth order the name Polybranches [Polybranchia], intending to indicate that the organs of respiration are subdivided into a fairly large number of small gills, but its principal characteristic is actually that these organs arranged in two rows, on each side of the animal’s body and completely exposed, what Mr. Cuvier designated under the name Nudibranches [Nudibranchia], which could even be preserved without inconvenience. … ’, and on the same page it is unambiguously stated that ‘ … the genus Doris Mr. Blainville places in particular order [which on the page 178 is designated as the order Cyclobranches] ’. Thus, regardless of the implied taxonomic content of Nudibranchia by Cuvier, Blainville immediately distinguished these two major body plans at the order level, not just as suborders or families. In a further work, Blainville (1816: 51 – 53) explicitly listed in the details for his order Polybranchia several core genera, including Glaucus, Tergipe s, Eolidia, Scyllaea, Tritonia, and Thetys, thus undoubtedly covering the major diversity of the Nudibranchia without dorids. Cuvier (1817: 389), instead, further reinforced the lumped classification by the unexplained complete omission of Blainville’s two ordinal system, and furthermore, by the incorrect usage of Blainville’s dorid’s order Cyclobranchia, for very different and distantly related patellids and chitons (Cuvier 1817: 451). Therefore, the original diagnosis for Nudibranchia, with the initial explicit removal of the dorids (Blainville 1814: 177, not subsequent diagnosis byCuvier 1817: 389), almost ideally fits into the 170 - year later concept of ‘ Cladobranchia Willan and Morton, 1984 ’, which unambiguously implied the same diagnosis of the possession of numerous secondary respiratory processes on both sides of the body, either branched or not, but not a true dorid’s gill. Wägele and Willan (2000: 89) also clearly indicated that Nudibranchia has been renamed to Cladobranchia by Willan and Morton (1984) for the traditional suborders Dendronotacea, Arminacea, and Aeolidacea, exactly to accommodate the two-order system by Minichev (1970: 176), who explicitly used order Anthobranchia for dorids, and order Nudibranchia for traditional aeolidaceans, dendronotaceans, and arminaceans: ‘ Minichev called his clades Anthobranchia (for the dorids) and Nudibranchia (renamed Cladobranchia by Willan and Morton 1984) for the aeolids, arminids and dendronotaceans’. Given the enormity of hidden diversity at a very fine scale (Martynov and Korshunova 2022, Korshunova and Martynov 2024) worldwide that still awaits description in all organismal group, it is especially important to accurately separate drastically different patterns of major organizations at a higher scale, such as Nudibranchia and Doridida. This separation was performed at the initial ‘ joined’ description of the orders Nudibranchia (Polybranchia) and Doridida (Cyclobranchia) in Blainville (1814), and there are no historical, morphological, or phylogenetic reasons to dismiss that insightful initial designation. Herein, therefore, the order Nudibranchia is restricted (= Cladobranchia Willan and Morton, 1984) to the taxa without a true gill, thus restoring the original designation by Blainville (1814) without dorids. Respectively, the full ordinal status for the order Doridida is reinstated. Pelseneer (1894) was probably the first to clearly apply the name with the stem ‘ Dorid- ’ as a taxon above the family group (as a taxon ‘ Doridiens’, yet within ‘ Nudibranches’ s. l.). Therefore the authorship of the order Doridida, ordinal status restored, is assigned to Pelseneer (1894). For morphological diagnoses, and a list of included families for the order Doridida, see Martynov (2011), Korshunova et al. 2020 a, and Martynov and Korshunova (2025). According to ontogenetic data (Martynov 2011, Martynov et al. 2022), the order Nudibranchia is well differentiated from the order Doridida initially by separated rhinophores, which in the course of subsequent evolution may be secondarily united [for a comparison of patterns of the families Doridoxidae and Arminidae, see details in Korshunova and Martynov (2020)]. We have consistently applied the two-order system of nudibranchs, order Nudibranchia and order Doridida, respectively, throughout a series of our works (e. g. Martynov and Korshunova 2011, 2012, Martynov et al. 2022), including molecular phylogenetic analyses, Korshunova et al. 2017 a, 2020 a). The reinstated, monophyletic suborder Aeolidacea (Figs 1, 2) belongs to the restricted order Nudibranchia, along with the traditional suborders Arminacea Odhner, 1934 and Dendronotacea Odhner, 1934, both are definitely heterogeneous and paraphyletic (Goodheart et al. 2018, Korshunova and Martynov 2020, Karmeinski et al. 2021, Knutson 2021). Therefore, to further properly delineate the suborder Aeolidacea, the following suborders need to be restricted and reinstated within the proper Nudibranchia:	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFBAFFD2FCA5FDB5FADCFCAE.taxon	diagnosis	Diagnosis: Body bears dorsal cerata (papillae) of various lengths, number and pattern of placement, but basically in two sets of commonly numerous, partly crowded or, rarely, few in number, separately placed cerata dorso-laterally across almost the entire body length. The initial connection of separated rhinophores with broad oral veil almost completely reduced; rhinophores in adult state commonly closely placed. In an absolute majority of superfamilies, a fully functional single cnidosac (a storage area for nematocysts, which are stinging cells ingested for self-defence from cnidarian prey) is present in the apical part of the cerata. Very rarely the cnidosac is secondarily reduced. Branched appendages or gill-like structures are absent. Digestive gland in all superfamilies is branched in various degrees and patterns, including regular, simple rows. Anal opening may found on the right lateral side of the body (pleuroproctic), in between the anterior and posterior digestive gland branches on the right side of the body (acleioproctic), or between the branches of the posterior digestive gland on the right side of the body (cleioproctic), or very rarely placed toward the posterior extreme of the body. There are also some mixed states of anal opening placement. Jaws are found as a pair of whole, strong plates placed inside of each lateral side of the pharynx. Masticatory edges of the jaws bear various denticle-like structures in various patterns, or, more rarely, smooth. Radula formula falls into three main patterns: oligoserial (commonly more than one and less than 10 longitudinal rows of lateral teeth flank central teeth from each side), triserial (one longitudinal row of lateral teeth on each side of central teeth), and uniserial (lateral teeth completely reduced). Oligoserial is a very rare pattern within Aeolidacea, the majority of superfamilies possess either triserial or uniseral radula. Central (= rachidian) teeth usually with central cusp and various numbers and shapes of lateral denticles. In some families central teeth become pectinate, where the central cusp is reduced and may become almost indistinguishable. In a unique case, uniserial radular teeth are fused together in a continuous ribbon-like pattern. So far, there are no known cases within Aeolidacea where the radula is completely reduced. Reproductive system described as commonly diaulic, but there are patterns in various superfamilies that can be similar to a triaulic condition. Both distal and proximal seminal receptaculums, or only a single, distal or proximal receptaculum, present. If a single receptaculum is present, it is more commonly a distal receptaculum. Prostate rarely elaborate, evidently granulated, more commonly forms a prostatic vas deferens, but vas deferens and prostate itself in many cases remain relatively distinct. Copulative apparatus commonly includes entire, contractable, but usually non-evertable, penis of various shapes and lengths. Extremely rarely (in at least one taxon of the family Notaeolidiidae and in the genus Paracoryphella of the family Paracoryphellidae) the penis is directly attached to the external body wall. In different families, the penis may bear various hard structures, such as single or multiple stylets, or soft structures, such as warts, tubercles, or folds. Copulative apparatus may also include various glands, which form, in one particular superfamily, a special supplementary gland inserted to the vas deferens or penis, whereas in others form different accessory glands. Remarks: As a main result of the present study what follows is an updated system of the aeolidacean superfamilies and a Synopsis of all the aeolidacean families so far known, derived from the molecular phylogenetic analysis, which included all the families so far known, and two newly described aeolidacean families (Figs 1, 2). In a tight connection with the reliable comparison of the two new families from different aeolidacean lineages (Fig. 2) with all other aeolidacean family-level taxa, it needs to be specially highlighted that the current system of superfamilies of aeolidacean nudibranchs employed in the World Register of Marine Species (WoRMS 2024) is inconsistent with existing morphological and molecular data (see Results, and Synopsis below, including diagnoses of the new families; Figs 1, 2; Tables 1, 2). One of the major inconsistencies is that a number of families that belong to respective phylogenetically clearly distinct clades and correspond to morphological aeolidacean supergroups, such as Fionoidea, Flabellinoidea, and Aeolidioidea (Fig. 2), currently are chaotically scattered among the only two currently recognized superfamilies, Aeolidioidea and Fionoidea. For example, the core flabellinoideans of the families Coryphellidae and Paracoryphellidae (see Results andFigs 1, 2), for some reason are currently placed in WoRMS (2024) within a completely different morphological and molecular superfamily Fionoidea. Whereas, simultaneously, the actual Flabellinidae are definitely closer to the above-mentioned Coryphellidae and Paracoryphellidae than to any aeolidioidean families (Fig. 2), but for some equally unexplained reason they are placed instead into a very different molecular and morphological superfamily Aeolidioidea (WoRMS 2024). To counter this synonymization, over the past seven years we have presented several comprehensive aeolidacean phylogenies, which included all previously known and newly described families (Korshunova et al. 2017 a, 2019 b, Martynov et al. 2020, present study; Figs 1, 2). Therefore, we now have a sufficient basis for a superfamilies-based classification of Aeolidacea. In those previous, and these present, phylogenies, no representatives of the core of the main superfamilies Flabellinoidea, Aeolidioidea, and Fionoidea have been mixed with each other and all three major supergroups are monophyletic with high support (Figs 1, 2). The genus Edmundsella, which previously has shown some paraphyly with regard to other families (Goodheart et al. 2018), is invariably placed as an integral part of the monophyletic family Flabellinidae with the inclusion of the family stem-genus Flabellina (Korshunova et al. 2017 a, present study; Figs 1, 2) and consistently nested within other flabellinoids, but not with any other Fionoidea (Figs 1, 2). In turn, Flabellinopsidae are invariably placed as sister to the majority of core Flabellinoidea, but never with the family Notaeolidiidae (Korshunova et al. 2017 a, present study; Figs 1, 2). Therefore, the load of accumulated inconsistencies in the superfamily-based classification of the suborder Aeolidacea is currently so high that while we have separated two new taxa at the family-level (see below) in the present study, further progress in aeolidacean nudibranch phylogeny and classification is impossible without proper resolution of the above-mentioned serious objective contradiction in the superfamily-based classification of aeolidacean nudibranchs. Thus, before further comparison of the Hantazuidae fam. nov. and Chudidae fam. nov. (which are definitely distinctly different from any aeolidacean families — see diagnoses and descriptions in the Synopsis below; Figs 1, 2; Tables 1, 2) can be presented, we need to clarify the superfamily system of the suborder Aeolidacea. Fortunately, separation of the superfamilies is a nomenclaturally relatively easy action because according to ICZN (1999, article 36), and to the principle of coordination, a taxon of any rank in the family group, including superfamily, ‘ is deemed to have been simultaneously established for nominal taxa at all other ranks in the family group’, with the same genus-derived stem family-group name and, importantly, the same authorship. Thus, using the accumulated comprehensive morphological and phylogenetic data on aeolidacean nudibranchs, we may now refine the aeolidacean superfamily system. First, we separate and consider valid three major aeolidacean superfamilies, all of them having been previously supported for a sufficiently long time (Bouchet et al. 2005, 2017; even with considerable reservations for the position of several families, see below) and in all of them, consistent morphological data align with evidently distinct phylogenetic clades (Korshunova et al. 2017 a, present study; Fig. 2): Flabellinoidea Bergh, 1889, Aeolidioidea Gray, 1827, and Fionoidea Gray, 1857. The triserial superfamily Flabellinoidea Bergh, 1889, reinstated, contains exclusively triserial families without a special supplementary gland in the male part of the hermaphroditic reproductive system (with the exception of a partly similar accessory gland in the coryphellid genus Occidenthella, but clearly independently evolved from fionoideans and aeolidioideans, see below) — Coryphellidae, Paracoryphellidae, and Flabellinidae. In turn, the uniserial superfamily Aeolidioidea Gray, 1827 contains a majority of the exclusively uniserial families without a special supplementary gland (some taxa with additional glandular formations associated with the copulative apparatus, independently evolved from fionoids) — Aeolidiidae, Myrrhinidae, Facelinidae, Favorinidae, Glaucidae, Babakinidae, and Pleurolidiidae. The triserial family Chudidae fam. nov., discovered through our present work, shows some relation to Aeolidioidea, but also aligns as a sister-taxon to several other Aeolidacean superfamilies (Figs 1, 2), and thus cannot be unambiguously placed into any of the known or aeolidacean superfamilies (Fig. 2; see detailed discussion below) established here; therefore, is placed in a separate superfamily Chudoidea superfam. nov. (Figs 1, 2). Finally, the third largest aeolidacean superfamily, the predominantly uniserial superfamily Fionoidea Gray, 1857 contains a majority of the exclusively uniserial families with a special supplementary gland in the copulative apparatus (inserted more commonly into the penis or, more rarely, into the vas deferens) — Abronicidae, Murmaniidae, Xenocratenidae, Cuthonellidae, Calmidae, Cuthonidae, Tergipedidae, and Trinchesiidae. Paradoxically, within Fionoidea there is only a single family without a special supplementary gland and, notably, with a uniserial radula — the family Fionidae (the superfamily stem-genus Fiona bearing its name), but only a single triserial family, Eubranchidae (Figs 1, 2). However, apart from these three major aeolidacean superfamilies, there are several family-level taxa that cannot be included in any of these three major supergroups according to morphological and molecular data (Figs 1, 2). The classificatory placement of these families according to their current superfamily position in WoRMS (2024) is also highly inconsistent. For example, two of the most basally placed aeolidacean triserial families, Apataidae and Samlidae — with disparate ceratal placement morphology and differing details of their reproductive systems — for some inexplicable reason are placed within the predominantly uniserial Fionoidea whose phylogenetic position is obviously very distant to Apataidae and Samlidae (Figs 1, 2). The same is true for the triserial Cumanotidae, whose phylogenetic position, together with their paedomorphic sister-family Pseudovermidae (Martynov et al. 2020), do not show a definite relationship to any main aeolidacean superfamily or other family (Fig. 2) according to all available analyses (Martynov et al. 2020, present study; Fig. 1), but for some equally inexplicable reason are currently placed within the predominantly uniserial Fionoidea, which are obviously not directly related to the superfamily Cumanotidae. Furthermore, the triserial family Flabellinopsidae, together with the robustly morphologically and molecular confirmed (Fig. 2) uniserial family Hantazuidae fam. nov. (Fig. 2, see below), align as sister to the superfamily, Flabellinoidea, but without significant support (Fig. 1). Externally both the triserial Flabellinopsidae and the uniserial Hantazuidae fam. nov. are partly similar in the possession of a flap-like — rather than only discontinuous — notal edge or stalk-like ceratal peduncles of Flabellinoidea. But partly similar flaps may occur in core species of the otherwise distantly related (Figs 1, 2) Notaeolidiidae (Wägele 1990) family with an oligoserial radula. That external feature may not indicate a close relationship, but instead may have very ancient evolutionary roots for Aeolidacea, so that feature must be considered in the Aeolidacea superfamily classification. Additionally, the family Flabellinopsidae obviously shows a more distantly-related position compared to the core Flabellinoidea family, Flabellinidae, according to phylogenomic analysis (e. g. Karmeinski et al. 2021), and this provides additional justification of the more significant separation between core Flabellinoidea (Paracoryphellidae, Flabellinidae, and Coryphellidae) species and Flabellinopsidae. Therefore, taking into consideration the molecularly robust support between the triserial Flabellinopsidae and the uniserial Hantazuidae fam. nov. (Figs 1, 2), the morphological disparity between Flabellinopsidae and Hantazuidae fam. nov. on the one hand, and the core triserial families Paracoryphellidae, Flabellinidae, and Coryphellidae (superfamily Flabellinoidea) on the other hand, we have established the separate superfamily Flabellinopsoidea Korshunova et al., 2017 for the families Flabellinopsidae and Hantazuidae fam. nov. (Fig. 1). Ultimately, one of the most basal aeolidacean families, the family Notaeolidiidae (which aligns as sister to the family Samlidae, and together with Apataidae is sister to all other Aeolidacean families; Fig. 2), has the pattern of an oligoserial radula with more than one and less than 10 regular longitudinal rows of lateral teeth per each side, which is unknown in any other aeolidaceanfamily (seeTables 1,2). Nevertheless, Notaeolidiidae are currently placed in the drastically morphologically different, exclusively uniserial superfamily Aeolidioidea in WoRMS (2024). Considering all these obvious morphological and molecular inconsistencies, along with the above-outlined three major aeolidacean superfamilies, we recognize the following ‘ lesser’ aeolidacean superfamilies: Notaeolidioidea Eliot, 1910, Samloidea Korshunova et al., 2017, Apataoidea Korshunova et al., 2017, Unidentioidea Millen and Hermosillo, 2012, Cumanotoidea Odhner, 1907 (apart from Cumanotidae also to include its paedomorphic close relatives Pseudovermidae, see: Martynov et al. 2020), and Flabellinopsoidea Korshunova et al., 2017. The position of two smaller families with long-discussed uncertain positions such as Embletoniidae (Karmienski et al. 2021) and ‘ Piseinotecidae’ (Korshunova et al. 2017 a), plus a few more uncertain taxa, are considered further in the present study (see Synopsis of all aeolidacean superfamilies and families below). The separation of several ‘ lesser’ superfamilies within Aeolidacea is not pursued to perform classic ‘ classificatory division’, but clearly aims to maximally reflect the extremely complex, genuine evolutionary patterns within Aeolidacea (Fig. 1), uncovered in all the performed analyses up to this point. Nearly all families are traditionally assessed as having strict distinct correspondence to particular family-level taxa features, such as patterns of the notal edge, position of the anus, a triserial or uniserial radula (e. g. Odhner 1934, Odhner in Franc 1968), and other characters that are distributed over family-level aeolidacean groups in a highly intricate, sometimes counter-intuitive pattern, forming an evolutionary-fuelled morphological and molecular immensely complicated picture (Figs 1, 2). This complexity must be correspondingly reflected in the respective family- and superfamily-based revised Aeolidacean taxonomy. The family Embletoniidae Pruvot-Fol, 1954 shows a somewhat unsettled phylogenetic relationship to Aeolidacea (see: Martynov et al. 2020, Karmeinski et al. 2021) and is included in the present Synopsis as a separate superfamily addition, after all other aeolidacean superfamilies. The updated Synopsis with the diagnoses of all of the abovediscussed valid aeolidacean superfamilies and families of the suborder Aeolidacea is, therefore, presented below and throughout the text. Further data may potentially correct some aspects of this classification of superfamilies, but according to the currently available extensive morphological data and robustly supported numerous aeolidacean phylogenetic superfamily clades (Fig. 1), this classification scheme has a reliable evolutionary basis. In the future, more detailed genomic data may add further details to some of these clades and respective groups, but it is unlikely that it will change the major patterns of aeolidacean phylogeny. For example, the later phylogenomic study of Karmeinski et al. (2021) largely confirmed the major aeolidacean family-level clades originally revealed in Korshunova et al. (2017 a). Superfamilies included: Notaeolidioidea Eliot, 1910, reinstated; Samloidea Korshunova et al., 2017, herein established; Apataoidea Korshunova et al., 2017, herein established; Unidentioidea Millen and Hermosillo, 2012, herein established; Fionoidea Gray, 1857, restricted; Cumanotoidea Odhner, 1907, herein established; Chudoidea superfam. nov.; Aeolidioidea Gray, 1827, restricted; Flabellinopsoidea Korshunova et al., 2017, herein established; Flabellinoidea Bergh, 1889, reinstated. Synopsis of the suborder Aeolidacea	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF4FF96FF21FE16FA5DFB50.taxon	description	(Figs 1, 2, 13, 18; Table 5) Korshunova et al. 2017 a: 43 – 4. Korshunova et al. 2017 b: 140. Type species: Coryphella trilineata O’Donoghue, 1921. Diagnosis: Body moderately narrow. Notal edge discontinuous. Cerata in several groups. Rhinophores distinctly annulate in the type, and core Orienthella s. s., and annulate to tuberculate in Orienthella s. l.. Anterior foot corners present. Central teeth with compressed narrow cusp and distinct short denticles in type and closely related sister-species. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens short, expands into a broad penial sheath with an additional glandular formation, but not as an protruding accessory gland, prostate indistinct. Penis triangular, folded. Species included: Orienthella trilineata (O’Donoghue, 1921) comb. nov. (with additional external and radular data; Fig. 18), Orienthella piunca (Marcus Er., 1961) comb. nov. (= Coryphella fisheri MacFarland, 1966), Orienthella (?) cooperi (Cockerell, 1901) comb. nov., Orienthella (?) fogata (Millen and Hermosillo, 2007) comb. nov., and Orienthella (?) verta (Marcus, 1970) comb. nov .. Remarks: All Orienthella species constitute a highly-supported clade (PP = 1, BS = 91; Figs. 1, 13), including the separate distinct clades Orienthella trilineata, O. piunca comb. nov., O. cf. verta, O. cooperi, and O. fogata. Uncorrected COI p - distances within the O. trilineata clade are 0 – 2.3 %, and within the O. piunca comb. nov. clade are 0 – 1.7 %. Uncorrected COI p - distances between the O. trilineata and O. piunca comb. nov. clades are 7.9 % – 9.6 %. The genus Orienthella with representative taxon from warmer subtropical-boreal water, or even partly tropical water, is rare for a coryphellid. The genus Orienthella in its precise sense (Orienthella s. s.), by combination of a discontinuous notal edge, annulate rhinophores, and compressed cusp of the central teeth, well differs from all other coryphellid genera. However, because molecular data are still unavailable or ambiguous and not well-supported by morphological data for several warm-water Coryphellidae, the real taxonomic situation, as a result, may be more complex, with more genera needing to be separated in future (therefore, currently considered ‘ Orienthella s. l. ’). Remarkably, by using finely differentiated genus-level taxonomy when the molecular data were not yet available, in Korshunova et al. (2017 a) we accurately predicted the position of at least two species as closely related to the genus Orienthella using only morphological data: namely O. cooperi (original description in Cockerell 1901) and O. fogata (original description in: Millen and Hermosillo 2007) (see Fig. 13, the predicted taxa are indicated by tick marks on the phylogenetic tree). The molecular phylogenetic placement for these two species appeared seven years later in Ekimova et al. (2024) as sister-clade to O. trilineata, O. piunca, and O. cf. verta (Fig. 13) and, therefore, we fundamentally predicted the position of O. cooperi and O. fogata as close to the proper Orienthella (Korshunova et al. 2017 a) using, exclusively, the fine-scale taxonomic differentiation of the genus Orienthella and other coryphellid genera (see: Korshunova et al. 2017 a; detailed Synopsis of all the genera of the family Coryphellidae; Figs 1, 13; Table 5). However, from a fine-scale taxonomic perspective, the species O. cooperi and O. verta do not match at an absolutely exact scale to the maximally narrowly defined Orienthella with the characters of two closely related species, the type species O. trilineata, and its close sister-species O. piunca, because O. cooperi has irregularly tuberculate, instead of annulate, rhinophores, and for O. verta smooth rhinophores have been reported (Millen and Hermosillo 2007). However, O. fogata (Fig. 13), a close sister-species to O. cooperi, also has somewhat irregular annulation on the rhinophores, compared to the distinct annulations in the type species O. trilineata (Fig. 18 C, D). Taking also into consideration some differences in the descriptions of the central teeth of the radula in O. cooperi and O. fogata, it is better to separate a new genus for at least the latter two species in order to make an absolutely precise genus-level unit for this group. We refrain from creating a new genus for O. cooperi and O. fogata in the present article since we do not have our own material to thoroughly study all the morphological details. We also only temporarily include ‘ Coryphella ’ verta Ev. Marcus, 1970 into the the somewhat more broadly understood genus Orienthella (Fig. 13) due to its inconsistent rhinophoral morphology (Marcus 1970, Millen and Hamann 2006) and the unavailability of relevant material for checking morphological and molecular data. Only a single COI sequence is present in GenBank, for which no morphological confirmation was obtained from specimens with verified morphology of true O. verta. However, the original diagnosis of Orienthella inKorshunova et al. (2017 a) included both annulate and tuberculate rhinophores, and, therefore, the confirmation of O. cooperi and O. fogata as phylogenetically closely related to the proper genus Orienthella seven years after Korshunova et al. (2017 a) (Fig. 13 predicted taxa indicated by tick marks) definitely demonstrates the high reliability and practical usefulness of the finely differentiated genus-level systematics of the family Coryphellidae. It is also remarkable that even after the addition of novel data, the position of the genus Occidenthella not only did not change, but significantly strengthened since the genus was initially proposed in Korshunova et al. (2017 a). The distinctness and obvious differences between the ‘ Western Pacific genus’ (noted in the genus name Occidenthella) and the ‘ Eastern Pacific genus’ (noted in the genus name Orienthella) is now robustly confirmed (Figs 1, 2, 13). No representatives of Orienthella have yet been discovered in the Western Pacific, and likewise no representatives of Occidenthella have yet been discovered in the Eastern Pacific (Synopsis; Figs 1, 2, 13; Table 5), despite the potential possibility, especially due to anthropogenic transportation. cerata. M, details of rhinophores. N, radular teeth, anterior part of radula, SEM. O, radular teeth, posterior part of radula, SEM. P, radular teeth, details of posterior part of radula, SEM. Q, jaw, SEM. R, details of masticatory process of jaw, SEM. S, details of masticatory process of jaw, SEM. Portorchardia candela gen. et sp. nov. Paratype KM 953, Port Townsend, Washington, USA (T – Y) 20 mm length (live). T, living animal on substrate. U, radular teeth, anterior part of radula, SEM. V, radular teeth, posterior part of radula, SEM. W, radular teeth, details of posterior lateral teeth, SEM. X, details of masticatory process of jaw, SEM. Y, details of masticatory process of jaw, SEM. Z, scheme of reproductive system. Scale bars: E, 100 μm; F, 10 μm; G, 100 μm; H, 50 μm; I, 10 μm; N, 50 μm; O, 100 μm; P, 20 μm; Q, 100 μm; R, 20 μm; S, 5 μm; U, 50 μm; V, 20 μm; W, 10 μm; X, 20 μm; Y, 10 μm; Z, 0.5 mm. Photos: Karin Fletcher. SEM Images: Alexander Martynov. Abbreviations: a, ampulla; fgm, female gland mass; p, penis; psh, penial sheath; rsd, receptaculum seminis distal; rsp, receptaculum seminis proximal; vd, vas deferens. In the present study, we also confirm the heterogeneity within true Orienthella, and along with the type species Orienthella trilineata (O’Donoghue, 1921) (original description in: O’Donoghue 1921) we have resurrected the sister-species Orienthella piunca (Marcus Er., 1961) comb. nov. (= Coryphella fisheri MacFarland, 1966). Both Orienthella trilineata and Orienthella piunca form distinct clades according to the molecular phylogenetic data (Fig. 1, 13). Morphologically, O. trilineata can be distinguished from O. piunca by its paler coloration in which the orange pigment on the rhinophores and oral tentacles is lacking or insignificant (O’Donoghue 1921, present study; Fig. 18 A – D). In the present study, additional data for the true Orienthella trilineata are presented and the neotype is selected (Fig. 18 A – I). To provide robust taxonomic assessment, neotype KM 1069, 10 mm length (live), for O. trilineata is selected here from Rich Passage, Washington, USA, collected on 16 January 2017 by Karin Fletcher at the depth 20.1 m, from the geographic region close to the type locality in southern part of British Columbia (Canada) (O’Donoghue 1921), from essentially same depth range. The external, jaws, and radular characters of the neotype are presented in Figure 18 A – I. Marcus (1961) did not present a description completely consistent with the actual coloration because his study relied mostly on preserved specimens and greatly overstated the rhinophoral variability (also partly due to the usage of preserved specimens); however, otherwise ‘ Coryphella ’ piunca fits into the true Orienthella genus by details of its external morphology, the presence of a compressed cusp of the central teeth, and its reproductive system morphology. MacFarland (1966), though, described coloration for his ‘ C. ’ fisheri (currently considered a synonym of O. trilineata s. l.) as commonly with orange-tipped rhinophores, but he also mentioned some colour variability, and figured central teeth of radula under a lateral view. Instead, Marcus (1961) for the figured specimen of ‘ C. ’ piunca unequivocally presented distinct annulations of rhinophores and compressed cusp of the central teeth. Thus, ‘ C. ’ piunca well corresponds to Orienthella s. s.. Furthermore, despite that Marcus described the coloration of the living animal imprecisely, he clearly mentioned three lines on the body of ‘ C. ’ piunca. Taking into consideration that both Marcus’s (1961) ‘ C. ’ piunca and MacFarland’s (1966) ‘ C. ’ fisheri came from essentially similar type localities in Northern California, and that true O. trilineata has not yet been confirmed for the type localities of both ‘ C. ’ piunca and ‘ C. ’ fisheri (Fig. 13), the external and internal characters of ‘ C. ’ piunca unambiguously indicate its placement within Orienthella s. s.. Given the precedence of ‘ C. ’ piunca Marcus, 1961 over ‘ C. ’ fisheri MacFarland, 1966, it is correct to apply the name Orienthella piunca (Marcus Er., 1961) comb. nov. to the former Orienthella wrongly assigned to O. ‘ trilineata ’ with a more southern distribution plus commonly having orange-tipped rhinophores and oral tentacles (Behrens et al. 2022). ‘ Coryphella ’ fisheri MacFarland, 1966 (original description in: MacFarland 1966), therefore, is a synonym of Orienthella piunca (Marcus Er., 1961) comb. nov .. Such a north – south gradient in distribution with the southern biogeographic boundary of the more northern species around Oregon – Northern California is quite characteristics for several NE Pacific nudibranchs, particularly the pairs Dendronotus robilliardi Korshunova et al., 2016 (northern) – D. albus MacFarland, 1966 (southern) (with a reservation that D. robilliardi and D. albus overlap in their range around the BC – WA regions) and Catriona columbiana (O’Donoghue, 1922) (northern) – Catriona spadix (MacFarland, 1966) (southern) (Korshunova et al. 2016, 2022). The latter case is in turn very similar to the distribution of Orienthella trilineata and Orienthella piunca. Therefore, ‘ C. ’ piunca Marcus, 1961 with type localities in Dillon beach and Monterey Bay in Northern California (and its synonym ‘ C. ’ fisheri MacFarland, 1966 from Monterey Bay) is resurrected as Orienthella piunca (Marcus, 1961) comb. nov., which is sister to the proper Orienthella trilineata (O’Donoghue, 1921) (Fig. 13) with a distribution generally from the more southern parts of Alaska to Oregon, but its precise range still need to be investigated. Comparison of the genus Orienthella with all valid, currently included Coryphellidae genera is presented in Table 5.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8EFFE0FC40FA37FE5CFC9A.taxon	description	(Figs 1, 2, 5 B, 10, 11; Table 4)	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF8EFFE0FC40FA37FE5CFC9A.taxon	diagnosis	Diagnosis: Body wide. Notal edge present, well-defined, continuous. Cerata not stalked, in continuous numerous rows. Ceratal rows branched. Rhinophores smooth to wrinkled. Anus pleuroproctic under the notal edge. Commonly no elaborate oral glands. Masticatory edges of jaws bear several rows of compound, sharpened or tubercle-like denticles. Radula formula 1.1.1. Additional one to three rows of asymmetrically placed small, reduced lateral teeth may be present. Central teeth commonly with strong cusp, usually not compressed by adjacent lateral denticles in adult state in a majority of genera, except the genus Mgueolia. Lateral teeth narrow or with attenuated process basally, usually denticulated. Commonly only a single distal receptaculum seminis present, but two receptaculums may occur. Vas deferens always long, prostate tubular or elaborated, wide granulated. Accessory gland absent. Massive external permanent penial collar with internal penis inside presents in the genus Chlamylla. Penis unarmed, elongated conical, internal in majority of genera, or fully external in the genus Paracoryphella. Genera included. Chlamylla Bergh, 1886, Paracoryphella Miller, 1971, Polaria Korshunova et al., 2017, Ziminella Korshunova et al., 2017, and Mgueolia Korshunova et al., 2025. Remarks: The family Paracoryphellidae encompasses several notably ancestral, highly archaic features, as, for example, an invariably continuous notal edge, especially significantly pronounced in the genus Chlamylla, without distinct ceratal clusters or stalks, together with an invariably pleuroproctic anus toward the middle part of the lateral side of body. Furthermore, the genus Chlamylla is the only taxon within the suborder Aeolidacea (Korshunova et al. 2017 a) that possesses a massive, distinct external penial collar in combination with internal penis, which otherwise is present only within the order Pleurobranchida (Martynov and Schrödl 2008, Martynov et al. 2022), an order definitely ancestral to the order Nudibranchia. In this study, molecular data are presented for Chlamylla borealis orientalis (Volodchenko, 1941) for the first time. (Figs 1, 2; morphological data see: Korshunova et al. 2017 a). Moreover, a uniquely, deeply ancestral feature is preserved within the genus Paracoryphella — the penis is attached directly to the body wall. This feature is present invariably in all taxa of the order Acteonida (Martynov 2011), but is only known within the order Nudibranchia in one taxon of one of the basal-most families, Notaeolidiidae (Wägele 1990), and thus in a single genus within the family Paracoryphellidae, Paracoryphella (Korshunova et al. 2017 a). Herein we further describe in details the amazing discovery of Mgueolia almamater (Fig. 10), which, according to the present molecular phylogenetic analysis, is robustly placed within the family Paracoryphellidae, as a sister-genus to all the previously known paracoryphellid genera: Chlamylla Bergh, 1886, Paracoryphella Miller, 1971, Polaria Korshunova et al., 2017, and Ziminella Korshunova et al., 2017 (Figs 1, 2). Externally Mgueolia almamater is well suited to the family Paracoryphellidae (Fig 10 A – F), whereas internally, while Mgueolia almamater possesses a predominantly flabellinoidean (including Paracoryphellidae) triserial radula, the radular patterns (Fig 10 K – P) readily recall those in the very distantly related family, Eubranchidae, from a completely different superfamily, Fionoidea (see Synopsis above and Figs 1, 2). On the other hand, radular patterns of Mgueolia almamater partly approach the radula of the genus Carronella of the family Flabellinidae (Korshunova et al. 2017 a), which may imply how the distinct Flabellinidae radula has been formed during the evolutionary radiation of the superfamily Flabellinoidea. This is one more remarkable case, among several others already presented in this study (Synopsis, Figs 1, 2) that unequivocally and unambiguously confirms the profound multilevel mosaicism within novel taxa with unique patterns, which in turn undoubtedly demonstrates that any ‘ pan-lumping’ suggestion would obscure the immense, evolutionary-fuelled fine-scale natural diversity at every taxonomic level in the suborder Aeolidacea. The creation of the paracoryphellid genus Ziminella Korshunova et al., 2017, established as part of a major revision of the super-lumped ‘ genus Flabellina ’, included descriptions of two new species Ziminella abyssa Korshunova et al., 2017 and Ziminella circapolaris Korshunova et al., 2017, and provided data for Ziminella japonica (Volodchenko, 1941) (Korshunova et al. 2017 a). However, in Valdes et al. (2018), this morphological and molecularly highly consistent major rearrangement of the main taxonomic patterns of aeolidacean was rejected, despite that the tree in Valdes et al. (2018) had a fundamentally similar topology regarding major Coryphellidae, Flabellinidae, and Paracoryphellidae clades, as well as new species within the genus Ziminella. In this study we present molecular data for all currently recognized valid Ziminella species, Z. abyssa Korshunova et al., 2017, Z. circapolaris Korshunova et al., 2017, reinstated, Z. japonica (Voldochenko, 1941), Z. salmonacea (Couthouy, 1838), and Z. vrijenhoeki Valdes et al., 2018 (Fig. 5 B), and also for the first time morphological data for the true Z. japonica both from the NW and NE Pacific, including external, jaw, and radular morphology (Fig. 11). Furthermore, an absolute majority of the included species differ by their penial morphology, which was discovered more than 30 years ago (Martynov 1992 b), when unequivocal differences were shown between copulative apparatuses of the taxa that are currently recognized under the genus name Ziminella, Z. salmonacea, and Z. japonica, and further confirmed in Martynov (2012) and Korshunova et al. (2017 a). Despite this, Valdes et al. (2018) commented that allegedly ‘ no data’ were presented for penial morphology in the first description of Z. circapolaris, despite that in the original description of this species the data for the copulative apparatus were unequivocally provided (Korshunova et al. 2017 a: 22). At the same time, the data for the penial morphology for Z. vrijenhoeki provided in Valdes et al. (2018) was highly ambiguous: while in the description of Z. vrijenhoeki (Valdes et al. 2018: 415) it is described as ‘ penis simple, elongate’, but in the remarks to the description (Valdes et al. 2018: 420) it was described as ‘ folded’, whereas according to the figures (Valdes et al. 2018: figs 11, 12) the penis does not look to be especially ‘ folded’, and appears as rather an entire structure with a somewhat blunt tip. In the present study we also for the first time apply molecular data (Figs 1, 2, 5 В) to a group of populations closely related to the true Z. japonica, which also inhabits shallow water regions in the northern parts of NE Pacific, despite that its type locality is situated very distantly at moderate depths of c. 100 – 1000 m in the Sea of Japan and neighbouring waters. We also confirm that not only Z. salmonacea and Z. japonica, but also Z. circapolaris and Z. salmonacea are well distinguished by their penial morphology. Morphological data are supported by the results of the molecular-phylogenetic analyses. All Ziminella species constitute a highly-supported clade (PP = 1, BS = 100; Fig. 5 B). One NW Pacific and two NE Pacific Z. japonica formed a highly-supported clade (PP = 1, BS = 98), sister to the Z. vrijenhoeki clade (PP = 1, BS = 100). Uncorrected COI p - distances within the Z. japonica clade are 0.3 % – 0.6 % and within the Z. vrijenhoeki clade are 0 % – 0.3 %. The COI minimal uncorrected COI p - distance between Z. japonica and Z. vrijenhoeki is 8.1 %. Only COI data for Z. vrijenhoeki MIMB 42255 among all publicly available data were used due to possible contamination by Carronella pellucida data (for details see Supporting Information, Table S 2). Ziminella japonica and Z. vrijenhoeki clustered in two separate sister-clades that had the closest position to the clade, including Z. salmonacea and Z. circapolaris (PP = 1, BS = 100), but with low support (PP = 0.73, BS = 45). Ziminella circapolaris, reinstated formed a separate clade (PP = 1, BS = 100), but within the Z. salmonacea clade, which can be explained by the insufficient number of 16 S, H 3, and 28 S genes in the dataset and will be investigated in a separate study. Uncorrected COI p - distances within the Z. salmonacea clade are 0 – 1.1 % and within the Z. circapolaris clade is 0. The COI minimal uncorrected COI p - distance between Z. salmonacea and Z. circapolaris is 2.3 %. Ziminella abyssa clustered in a distinct separate clade, sister to Z. japonica, Z. vrijenhoeki, Z. salmonacea, and Z. circapolaris (Fig. 5 B). The COI minimal uncorrected p - distances between the Z. japonica clade and the Z. salmonacea, Z. circapolaris, and Z. abyssa clades are 15.3 %, 15.3 %, and 17.6 % respectively.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA0FFC0FE81FDB5FC37FD1C.taxon	description	(Figs 1, 4) urn: lsid: zoobank. org: act: 41 C 28779 - E 6 FB- 4524 - 8 CBF- F 35 A 226 E 519 D Type species: Piseinotecus soussi Tamsouri et al., 2014. Etymology: After a shorter variant of spelling ‘ Phetida’ attributed to the Ancient Greek sea goddess, Thetys, in reference to the ancient ocean, Thetys, which includes the modern Mediterranean Sea, to denote the Thetys-related origin of the new genus. Diagnosis: Body moderately narrow. Notal edge completely reduced. Cerata on indistinct stalk-like derivations of former notal edge. Rhinophores smooth. Anterior foot corners present. Anus pleuroproctic. Central teeth with narrow non-compressed cusp and distinct denticles, some cusps forked. Lateral teeth absent. Proximal receptaculum seminis. Moderately long vas deferens with very distinct, thickened non-granulated prostate. No external penial collar. Accessory gland absent. Penis conical, with a long, sabre-shaped curved stylet. Species included: Phetia soussi (Tamsouri et al., 2014) comb. nov. [original description in Tamsouri et al. (2014); for corrected morphological data see present study, Fig. 4]. Remarks: The new genus Phetia gen. nov. forms a distinct, maximally supported (PP = 1, BS = 100) separate clade, sister to all known tropical true Unidentia (Figs 1, 2). Uncorrected COI p - distances within the Phetia soussi comb. nov. clade are 0 – 0.17 %. The COI minimal uncorrected p - distance of 15.4 % was found between Phetia soussi comb. nov. and Unidentia sandramillenae, and 17.4 % between P. soussi comb. nov. and Pacifia goddardi.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF97FFF7FEF1FEF1FAC3FE87.taxon	description	(Figs 1, 2; Table 4) Protoaeolidiellidae Odhner in Franc 1968: 882. Diagnosis: Body narrow. Notal edge present, narrow. Ceratal rows branched, numerous non-elevated cerata per row. Rhinophores smooth. Anus pleuroproctic. Masticatory edges of the jaws moderately denticulated with single row of denticles. Radula formula 0.1.0. Central teeth arc-shaped, pectinate. Distal or proximal receptaculum seminis. Vas deferens short, prostate indistinct. Accessory gland absent. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Pleurolidia Burn, 1966 and Protaeolidiella Baba, 1955. Remarks: The family Pleurolidiidae and the following family Babakinidae are interesting cases because they represent either a relatively defined, or partly reduced, notal edge, which is a definite ancestral feature for all Nudibranchia [see Korshunova and Martynov (2020) for the character states’ discussion], and, respectively, remain within the few families of the superfamily Aeolidioidea. The presence of a notal edge in families within Aeolidioidea, otherwise a superfamily with a completely reduced notal edge, in combination with the ancestral-confirmed placement of a pleuroproctic anus (see: Korshunova and Martynov 2020) in both Pleurolidiidae and Babakinidae is illustrated in the phyloperiodic approach, in which quasiperiodic, ontogeny-based ancestral phylotypic features can be expected to be found in every higher level taxon such as family- and order-group. [See Martynov and Korshunova (2022) for discussion and presentation in this study of Phyloperiodic Tables, which align the three major aeolidacean oligoserial, triseral, and uniserial radular patterns with the results of molecular phylogenetic analysis (Figs 1, 2; Tables 1, 2)]. Therefore, while the well-defined notal edge (continuous or in various degree reduced or modified) is characteristic of the superfamily Flabellinoidea (see Synopsis below), its presence in reduced form in a few families of the superfamily Aeolidioidea, highlights the reliability of the Phyloperiodic Tables to explicitly present ancestrally preserved features, based on phylotypic periods confirmed by evolutionary development biology (e. g. Love 2024) for various disparate animal phyla. The ancestral notal area of non-aeolidacean nudibranchs possesses a well-defined, ample notal edge (Korshunova and Martynov 2020), and, therefore, this feature is an ontogenetically conserved character and persists in various forms, even in such crown-groups of the suborder Aeolidacea (Korshunova et al. 2017 a, present study; Figs 1, 2). It must also be noted that both Pleurolidiidae and Babakinidae either comprise only two genera or are monotypic, but in this case the separate status of these families, for some non-scientific reasons is ‘ allowed’, whereas the fundamentally similar cases of describing various finely differentiated families of the superfamily Fionoidea instead causes a strong ‘ revision-shock’ lumping reaction [see details in Korshunova et al. (2022) and Discussion].	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFE9FF88FEC9F88AFD42F88E.taxon	description	(Figs 1, 2, 13, 18) urn: lsid: zoobank. org: act: 6 BD 642 D 1 - 3178 - 4 B 72 - BD 01 - 908323 F 333 B 8 Holotype: KM 954, L = 32 mm (live), north-eastern Pacific, USA, Washington State, Salish Sea, Rich Passage, west of Point Glover, stones, 14 m depth, 9 April 2018, coll. K. Fletcher. Paratype: KM 953, L = 20 mm (live), north-eastern Pacific, USA, Washington State, Salish Sea, Point Hudson, Port Townsend, stones, 14.3 m depth, 21 May 2017, coll. K. Fletcher. Etymology: See above under the new genus name. Description External morphology (Fig. 18 J – M, T) Body moderately narrow. Foot and tail moderate, anterior foot corners moderately long. Oral tentacles long. Rhinophores c. 1.5 times shorter than oral tentacles, or similar to its in size, with c. 10 – 14 thickened, sometimes fully reduced annulations. Dorsal cerata finger-shaped to fusiform, forming several clusters along dorsal edges. Apices of cerata gradually pointed, with elongate cnidosacs. Digestive glanddiverticulumfillssignificantvolumeofcerata. Analopening on right side below middle cluster of cerata. Reproductive openings lateral, below first anterior cluster of cerata. Colour (Fig. 18 J – M, T) Background colour semi-transparent whitish to greyish. Branches of digestive system in cerata usually orange, orange-brownish to orange-reddish throughout most of the length with somewhat lighter, greyish bases. Cnidosacs in subapical parts of cerata yellowish-brownish or orange-brownish. Below bases of cnidosacs there may be a somewhat darker orange-reddish narrow area on cerata. Apical parts of cerata without opaque cap of white pigment. Rhinophores covered with whitish pigment over almost their entire length, apical areas of both rhinophores and oral tentacles may be covered with differing amounts of orange or orange-brownish pigment. White pigment lines on each oral tentacle are joined on head in front of rhinophores and then form a thin continuous white line that runs along dorsal side to the tail. Similar thin white line runs laterally on each side of body meeting with the dorsal line at the tail. Jaws (Fig. 18 Q – S, X, Y) Jaws oval-triangular. Edge of masticatory processes bears up to about 40 denticles that may form up to at least 10 longitudinal rows of tubercles from internal side, diminishing toward inner part of the jaw. Denticles at very edge of masticatory processes thickened, compound and bear several tubercles. Radula (Fig. 18 N – P, U – W) Radula formula in two specimens 13 – 15 × 1.1.1. Central teeth elongate-triangular with long, distinct non-compressed cusp. Central teeth bear up to at least nine well-defined, separate, long lateral denticles. Cusp moderately wide, strongly delineated from adjacent first lateral denticles. Lateral teeth broadly triangular with outer process distinctly attenuated posteriorly and up to at least 14 sharp, long denticles on internal edge. Reproductive system (Fig. 18 Z) Hermaphroditic duct leads to convoluted ampulla of about three whorls. Vas deferens short, distally attached to dorsal side of penial sheath, prostate indistinct. Penial sheath large, wide. Penis is a considerably folded. Oviduct connects through insemination duct into female gland complex. Proximal and distal receptaculum seminis elongate-oval placed at some distance to each other and distal receptaculum larger. Ecology: Shallow water, upper subtidal, stony environment. Distribution: So far known only from Washington, USA and British Columbia, Canada in the NE Pacific. Remarks: Three Portorchardia candela sp. nov. formed a separate highly-supported clade (PP = 1, BS = 100), and had the closest position to Fjordia, Gulenia, Himatina, and Corrupta gen. nov, but with low support (PP = 0.99, BS = 47; Fig. 13). Uncorrected COI p - distances within the P. candela sp. nov. clade are 0.6 % – 1.1 %. The COI minimal uncorrected p - distance of 9.3 % was found between the P. candela sp. nov. and Fjordia browni. The COI maximal uncorrected p - distance of 16.2 % was found between the P. candela sp. nov. and both Orienthella trilineata and Orienthella cf. verta. For more details see above after the new genus diagnosis. Nomina dubia that must be excluded from the family Coryphellidae:	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFF6FF89FC1CFA96FE94F881.taxon	description	(Figs 1, 2, 13, 18; Table 5) urn: lsid: zoobank. org: act: B 69 D 74 A 9 - 688 F- 4 B 04 - 981 A- D 8 CE 8 B 248089 Type species: Portorchardia candela sp. nov .. Etymology: The genus name Portorchardia is named in honour of Port Orchard, the residence town of Karin Fletcher, whose longterms efforts in collecting and observing nudibranchs in this area has led to the description of many remarkable nudibranch taxa, including this new genus. The new species’ name candela means ‘ candle’ and refers to the flame-like coloration of its rhinophores (see Remarks below). Diagnosis: Body moderately narrow. Notal edge discontinuous. Cerata in several groups. Rhinophores moderately annulate. Anterior foot corners present. Central teeth with non-compressed moderately wide cusp and distinct long denticles. Lateral teeth denticulated with attenuated process basally. Distal and proximal receptaculum seminis. Vas deferens short, expands into a broad penial sheath with folded penis, prostate indistinct. Species included: Portorchardia candela sp. nov .. Remarks: The new genus Portorchardia gen. nov. and new species Portorchardia candela gen. et sp. nov. represent a remarkable combination of external features (Fig. 18 J, K, T), which are partly similar to the genus Orienthella, and molecular phylogenetic data (Fig. 1, 2, 13), which firmly places Portorchardia gen. nov. as sister to the genera Gulenia, Fjordia, Corrupta gen. nov., and Himatina (Fig. 13), and not directly related to the Orienthella clade. However, externally Portorchardia gen. nov. and the type species of Orienthella are distinguished by the relatively narrower body in the latter and relatively less annulated rhinopores in the new genus (Fig. 18 M, T). According to the internal morphological data, the new genus Portorchardia gen. nov. differs from Orienthella, the genus it most closely externally resembles, by its distinctly non-compressed cusp of the central teeth and distinctly longer lateral denticles (Fig. 18 N – P, U – W). Despite that the teeth of ‘ C. ’ fisheri [the latter is junior synonym of Orienthella piunca (Marcus Er., 1961) comb. nov.] are laterally figured in MacFarland (1966), the morphology of the radula also matches the true Orienthella radula with shorter lateral denticles around a compressed cusp of the central teeth, and not Portorchardia with distinctly longer lateral denticles and a non-compressed cusp (Fig. 18 N – P, U – W). These data highlight both the importance of careful consideration of morphology in the molecular era and a multilevel organismal diversity system, without which the discovery of the remarkable conjunction of external similarity, internal morphological distinctness and distant genetic relationship between Portorchardia gen. nov. and Orienthella (Figs 13, 18) according to molecular data would be meaningless under the pan-lumping concept of ‘ Coryphella ’. Comparison of the new genus Portorchardia gen. nov. with all valid, currently included Coryphellidae genera is presented in Table 5. The Coryphellidae family potentially includes more undescribed taxa, especially among Northern and Eastern Pacific coryphellid species, which must be carefully recognized at the genus-level and established using fine-scale morphological and molecular data, instead of a broad, completely undiagnosable pan-lumping synonymization inconsistent with molecular phylogenetic data. In this respect, for example, ‘ Coryphella ’ abei Baba, 1987 [original description in (Baba 1987 b), Japan], which possesses a moderately broad body, cerata in groups, Y-shaped white mark on the head, smooth rhinophores, anterior foot corners, non-compressed relatively broad cusp of the central teeth with distinct lateral denticles, lateral teeth with moderately attenuated basal process, moderately long vas deferens with distinct prostate and conical penis, and apparently a single distal receptaculum according to the original description, therefore, could potentially be related either to the genera Himatina, Corrupta gen. nov., and Portorchardia gen. nov., or more distantly related to the genera Orienthella and Occidenthella, and, thus, probably represents a separate genus, which needs to be established in further work.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9EFFFEFC4FFCFBFC3CF833.taxon	description	(Figs 1, 2; Table 4) Thiele 1931: 454. Korshunova et al. 2017 a: 67, 72, 73, supplementary materials. Martynov et al. 2020: 1, 3, 12 – 15. Diagnosis: Body narrow, worm-shaped. Notal edge completely reduced. Cerata reduced in a few separate rows. Rhinophores and oral tentacles absent. Anus acleioproctic in anterior part of the body. Masticatory edges of jaws bear a single row of denticles. Radula formula 1.1.1. Central teeth broad, pectinate, cusps not compressed by adjacent lateral denticles. Lateral teeth denticulated, not broadened. Proximal receptaculum seminis. Vas deferens moderately long to short, prostate indistinct or distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Genera included: Pseudovermis Perejaslavtzeva, 1891. Remarks: The family Pseudovermidae is the apex of paedomorphic reduction within the suborder Aeolidacea, when its initially complex ancestral body, driven by evolution in the interstitial environment (see: Flammensbeck et al. 2019, Martynov et al. 2020), was modified into an almost worm-shaped form with completely reduced rhinophores and oral tentacles, and considerably reduced cerata. Despite its dramatically paedomorphic evolution-modified external form, internally Pseudovermidae possess a triserial radula whose general pattern corresponds well to the family Cumanotidae, and together with the robust molecular phylogenetic data (Martynov et al. 2020, present study; Figs 1, 2) allows Pseudovermidae to be firmly placed with Cumanotidae in the same superfamily Cumanotoidea.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB7FFCCFC4DFEAAFD74FE43.taxon	description	(Figs 1, 2; Table 4) ‘ Genus Flabellina sensu latissimo ’ Gosliner and Griffiths 1981: 105, 109 – 15.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB7FFCCFC4DFEAAFD74FE43.taxon	diagnosis	Diagnosis: Body narrow. Notal edge discontinuous or completely reduced. Cerata on low elevations, few per row. Ceratal rows branched. Rhinophores perfoliate. Anus pleuroproctic under the reduced notal edge or shifted toward the acleioproctic position. Jaws with masticatory edges bear a single or several moderate or strong denticles. Radula formula 1.1.1. Central teeth usually with strong cusp, rarely compressed by adjacent lateral denticles. Lateral teeth denticulated, basal lateral parts elongated. Distal and proximal receptaculum seminis or only a proximal receptaculum. Vas deferens usually short, to moderately long, prostate indistinct or distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, not considerably widened, unarmed. Genera: Samla Bergh, 1900, Luisella Korshunova et al., 2017. Superfamily Apataoidea Korshunova et al., 2017, herein established	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFB7FFCCFC4DFEAAFD74FE43.taxon	description	(Fig. 2; Tables 1 – 3) Diagnosis: Aeolidacean superfamily with triserial radula. Notal edge completely reduced. Cerata in distinct, regularly placed separate rows, somewhat elevated. Rhinophores perfoliate. Anus mixed (pleuroproctic in a higher acleioproctic position). Anterior foot corners present. Elaborate oral glands present. Jaws with masticatory edges bear several moderate denticles, tuberculate to more sharpened. Central teeth cusp compressed by adjacent lateral denticles. Lateral teeth smooth with moderately attenuated process basally. Distal receptaculum seminis. Clasping organ in female part of reproductive system absent. Vas deferens moderately long, prostate relatively distinct. Supplementary and accessory glands absent. Massive external permanent penial collar absent. Penis internal, narrow, unarmed. Families included: Apataidae Korshunova et al., 2017. Remarks: Although superfamilies Samloidea and Apataoidea are sister (Fig. 2), their recognition as separate superfamilies is highly justified by morphological data because the latter superfamily immediately differs from the former by patterns of the ceratal rows and the complete absence of a notal edge, features that are more similar to much more distantly related superfamilies Fionoidea and Aeolidioidea. Furthermore, according to the molecular phylogenetic data, the sister-relationship between Samloidea and Apataoidea does not align with the highest support, which also implies that both superfamilies together do not form a consistent, natural, molecular, and morphological taxon. Notably, in all phylogenies obtained herein, the superfamilies Samloidea and Apataoidea invariably align as sisters to all other aeolidacean taxa, which in turn may imply that both Samloidea and Apataoidea, although disparate and diverged, represent an earlier off-shoot of the evolutionary radiation of the suborder Aeolidacea, when a common triserial ancestor of the majority of the modern aeolidacean superfamilies initially separated from the oligoserial Notaeolidioidea-like common ancestor of the suborder Aeolidacea (see Synopsis above; Figs 1, 2).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9BFFFBFEF1FC79FACBF823.taxon	description	(Figs 1, 2; Table 4)	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9BFFFBFEF1FC79FACBF823.taxon	diagnosis	Diagnosis: Body narrow. Notal edge completely reduced. Ceratal rows simple. Single non-elevated cerata per row. Rhinophores smooth. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of simple sharpened denticles. Radula formula 0.1.0. Central teeth with strong cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens short, prostate indistinct. Supplementary gland present, inserts into penis. Massive external permanent penial collar absent. Penis internal, narrow, armed. Genera included: Tergipes Cuvier, 1805. Remarks: After the obvious morphological heterogeneity and molecularly strong inconsistences of the previous ‘ pan-lumping agent’, the genus Cuthona proper was explicitly described [see illustrative history in Korshunova et al. (2021)]. Similarly, by restricting actual natural evolutionary patterns with ad hoc, human-based proposals (see details in: Korshunova et al. 2022), a new super-lumping ‘ strategy’ has been invented, completely flattening the highly heterogenous and molecularly highly disparate ‘ genus Tenellia sensu latissimo ’ (Gosliner et al. 2018) to include almost all the diversity of the currently fine-scale differentiated family Trinchesiidae (see Synopsis below). In this respect, it was first argued, using morphological arguments (Martynov 1992 a, 2006 a, Miller 2004) more than 30 years ago and currently with extensive molecular phylogenetic data (Korshunova et al. 2017 a, c, 2018, 2021, 2022), that if a ‘ pan-lumping’ concept should dismiss nearly all the diversity of the superfamily Fionoidea, it must choose as its super-lumped group not ‘ Cuthona Alder and Hancock, 1855 ’, nor ‘ Tenellia Costa, 1866 ’ but the oldest genus, Tergipes Cuvier, 1805. This is particularly true for the pan-lumped genus ‘ Tenellia’ where the genus Tenellia proper [restricted to only a few species close to the type genus Tenellia adspersa (Nordmann, 1845), see Korshunova et al. (2022) within the family Trinchesiidae], which is superficially, and evidently convergently, externally similar to Tergipes (which is placed in a distantly related molecular phylogenetic clade, Figs 1, 2) acquired a reduced, strongly paedomorphic external appearance, but at the level of the reproductive system demonstrates the similar presence of a penial stylet (although of a different pattern) and insertion of the supplementary gland into the penis (the latter feature is not one that is indicative at the family-level, since it is present in several very different families of the superfamily Fionoidea, see Synopsis above and below). Therefore, if, as evidence ad absurdum to apply the flawed logic of pan-synonymization (Gosliner et al. 2018, Kim et al. 2024) the oldest - ‘ somewhat’ similar genus to Tenellia Costa, 1866 — Tergipes Cuvier, 1805 must be chosen to be truly consistent in the persistent attempts to disregard the many family and genera levels of the superfamily Fionoidea. As we have shown, these attempts contradict true natural, evolutionary-fuelled morphological and molecular diversity (Figs 1, 2). An example of these attempts is illustrated by the problematic genus Rubramoena Cella et al., 2016 with a somewhat unsettled phylogenetic position (but commonly part of the family Trinchesiidae), and morphology that does not principally differ from members of the family Trinchesiidae (Korshunova et al. 2017 a – c). However, Rubramoena has not been synonymized either with Tergipes or with ‘ Tenellia’, yet, for inexplicable reasons, the morphologically distinct genus Zelentia Korshunova et al., 2017, with a robust phylogenetic position as sister to a majority of the genera of Trinchesiidae (Fig. 5 A), has been incorrectly synonymyzed with the super-lumped ‘ Tenellia sensu latissimo ’ (Kim et al. 2024). Thus, there is no consistency about which taxa are ‘ synonymized’ and which are ‘ not synonymized’, and clearly personal bias was the guiding principle, rather than scientific results, when making taxonomic decisions in the latter case. Otherwise, the family Tergipedidae in its current restricted sense (see: Korshunova et al. 2017 c) well represents a highly coherent morphological and molecular fine-scale taxonomic family-level unit, whose phylogenetic placement suggests several independent acquisitions of highly reduced, paedomorphic morphology within the superfamily Fionoidea (Figs 1, 2; Tables 3, 4). Sea also Remarks under the family Facelinidae to clearly show a preconception-based taxonomic arrangement in Aeolidacea, where the separation of many families and genera are allowed in the superfamily Aeolidioidea, whereas within the superfamilies Fionoidea and Flabellinoidea (particularly, within the family Coryphellidae) — separation of many families and genera are denied for completely unsubstantiated reasons (see Synopsis below and Discussion).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9AFFFFFF09F9DCFAD5F946.taxon	description	(Figs 1, 2, 5 A; Table 4) Nordsieck, 1972: 5, 80.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFF9AFFFFFF09F9DCFAD5F946.taxon	diagnosis	Diagnosis: Body commonly moderate to narrow. Notal edge commonly completely reduced. Ceratal rows usually simple, numerous-to-few non-elevated cerata per row. Rhinophores smooth, rarely annulate. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of compound, tubercle-like or flattened denticles. Radula formula 0.1.0. Central teeth arc-shaped to more narrow, usually with strong to moderately distinct cusp not compressed by adjacent lateral denticles. Distal receptaculum seminis. Vas deferens usually short to moderate, prostate indistinct to moderately distinct. Supplementary gland present, inserts into penis, in all confirmed taxa, reports of putative ‘ absence’ of supplementary (= ‘ penial’) gland are erroneous and based on the failure to identify the existing supplementary gland. Massive external permanent penial collar absent. Penis internal, not considerably broadened, armed with hollow stylet. Stylet present in all confirmed taxa, commonly short, in some cases long. Genera included: Catriona Winckworth, 1941, reinstated, including species Catriona aurantia (Alder and Hancock, 1842) comb. nov., Catriona casha Gosliner and R. J. Griffiths, 1981 comb. nov., Catriona columbiana (O’Donoghue, 1922) comb. nov., Catriona gymnota (Couthouy, 1838) comb. nov., Catriona kishiwadensis Martynov et al., 2022 comb. nov., Catriona lonca Marcus, 1965 comb. nov. (see: Korshunova et al. 2022), Catriona lucerna Korshunova et al., 2022 comb. nov., Catriona maua Ev. Marcus and Er. Marcus 1960 comb. nov., Catriona osezakiensis Martynov et al., 2022 comb. nov., Catriona spadix (MacFarland, 1966) comb. nov., and further valid species: Catriona alpha (Baba and Hamatani, 1963), Catriona oba Ev. Marcus, 1970, Catriona rickettsi Behrens, 1984, ‘ Catriona ’ susa Ev. Marcus and Er. Marcus, 1960, Catriona tema Edmunds, 1968, ‘ Catriona ’ urquisa Er. Marcus, 1965 (see: Korshunova et al. 2022), ‘ Catriona ’ venusta (Baba, 1949), Diaphoreolis Iredale and O’Donoghue, 1923, reinstated, including species Diaphoreolis flavovulta (MacFarland, 1966) comb. nov., Diaphoreolis lagunae (O’Donoghue, 1926) comb. nov.,? Diaphoreolis scintillans (Miller, 1977) comb. nov., Diaphoreolis stipata (Alder and Hancock, 1843) comb. nov.,? Diaphoreolis veronicae (Verrill, 1880) comb. nov., Diaphoreolis viridis viridis (Forbes, 1840) comb. nov., Diaphoreolis viridis emeraldi Korshunova et al., 2023 comb. nov., Diaphoreolis zvezda Korshunova et al., 2023 comb. nov., Narraeolida Burn, 1961, reinstated, Narraeolida colmani Burn, 1961 comb. nov., Njurja Er. Marcus and Ev. Marcus, 1960, reinstated, Njurja netsica Er. Marcus and Ev. Marcus, 1960 comb. nov., Pinufius Er. Marcus and Ev. Marcus, 1960, Phestilla Bergh, 1874, reinstated, including species ‘ Phestilla ’ arnoldi Mehrotra and Caballer, 2024 comb. nov., ‘ Phestilla ’ chaetopterana (Ekimova et al., 2017) comb. nov, ‘ Phestilla ’ fuscostriata J. T. Hu et al., 2020 comb. nov., ‘ Phestilla ’ goniophaga J. T. Hu et al., 2020 comb. nov., Phestilla lugubris (Bergh, 1870) comb. nov., Phestilla melanobrachia Bergh, 1874 comb. nov., ‘ Phestilla ’ minor Rudman, 1981 comb. nov., Phestilla panamica Rudman, 1982 comb. nov., ‘ Phestilla ’ poritophages (Rudman, 1979) comb. nov., Phestilla sibogae Bergh, 1905 comb. nov., ‘ Phestilla ’ subodiosa A. Wang et al., 2020 comb. nov., ‘ Phestilla ’ viei Mehrotra et al., 2020 comb. nov., Tenellia Costa, 1866, restricted to only include the species Tenellia adspersa (Nordmann, 1845), Tenellia gotlandica Lundin et al., 2022, Tenellia pallida (Alder and Hancok, 1854) (and its possible synonym Tenellia fuscata (A. Gould, 1870), plus potential hidden diversity, no other species that are currently assigned to the pan-lumping ‘ Tenellia’ genus in WoRMS (2024) can be considered as belonging to that genus), Selva Edmunds, 1964, Subcuthona Baba, 1949 (type species S. pallida Baba, 1949), validity confirmed, Toorna Burn, 1964 reinstated, Toorna thelmae Burn, 1964 comb. nov., Trinchesia Ihering, 1879, reinstated [this genus pending revision, but, very importantly, no species from the current genus Trinchesia s. l. can be assigned to ‘ Tenellia’ or ‘ Cuthona’, those species do not belong to the closely related group Trinchesia s. s. type species T. caerulea (Montagu, 1804), and, therefore, potentially representing undescribed genera are placed below in quotation marks, the same presentations should be applied further in ‘ WoRMS’, where a question mark implies an insufficient description or doubts that it belongs in the family Trinchesiidae), ‘ Trinchesia ’ acinosa (Risbec, 1928) comb. nov., ‘ Trinchesia ’ adyarensis (Rao, 1952) comb. nov., ‘ Trinchesia ’ akibai (Baba, 1984) comb. nov., ‘ Trinchesia ’ albocrusta (MacFarland, 1966) comb. nov., ‘ Trinchesia ’ albopunctata Schmekel, 1968 comb. nov.,? ‘ Trinchesia ’ anandalei (Eliot, 1910) comb. nov., ‘ Trinchesia ’ anulata (Baba, 1949) comb. nov., ‘ Trinchesia ’ barbadiana Edmunds and Just, 1983 comb. nov., ‘ Trinchesia ’ beta (Baba and Abe, 1964) comb. nov., ‘ Trinchesia ’ boma Edmunds, 1970 comb. nov., ‘ Trinchesia’ bughaw (Kim and Gosliner, 2024) comb. nov., Trinchesia caerulea (Montagu, 1804) comb. nov., ‘ Trinchesia ’ catachroma (Burn, 1963) comb. nov., ‘ Trinchesia ’ correai (Ortea, Caballer and Moro, 2002) comb. nov., Trinchesia cuanensis Korshunova et al., 2019 comb. nov., ‘ Trinchesia ’ diminutiva (Gosliner, 1980) comb. nov. Trinchesia diljuvia Korshunova et al., 2019 comb. nov., ‘ Trinchesia ’ divanica Martynov, 2002 comb. nov., ‘ Trinchesia ’ diversicolor Baba, 1975 comb. nov., ‘ Trinchesia ’ fidenciae (Ortea et al., 1999) comb. nov., ‘ Trinchesia ’ foliata (Forbes and Goodsir, 1839) comb. nov., ‘ Trinchesia ’ futairo (Baba, 1963) comb. nov., ‘ Trinchesia ’ genovae (O’Donoghue, 1926) comb. nov., ‘ Trinchesia ’ granosa Schmekel, 1966 comb. nov., ‘ Trinchesia ’ hamanni (Behrens, 1987) comb. nov., ‘ Trinchesia ’ henrici (Eliot, 1916) comb. nov., ‘ Trinchesia ’ herrerai (Ortea et al., 2002) comb. nov, ‘ Trinchesia ’ hiranorum Martynov et al., 2015 comb. nov., ‘ Trinchesia ’ ilonae Schmekel, 1968 comb. nov., ‘ Trinchesia ’ iris (Edmunds and Just, 1983) comb. nov., ‘ Trinchesia ’ ivetteae (Gosliner and Bertsch, 2017) comb. nov., ‘ Trinchesia ’ kanga Edmunds, 1970 comb. nov., ‘ Trinchesia ’ kuiterorum (Rudman, 1981) comb. nov., ‘ Trinchesia ’ lenkae Martynov, 2002 comb. nov.,? ‘ Trinchesia ’ leopardina (Vayssiere, 1888) comb. nov., ‘ Trinchesia ’ longi (Behrens, 1985) comb. nov.,? ‘ Trinchesia ’ macquariensis Burn, 1973 comb. nov., ‘ Trinchesia ’ millenae (Hermosillo and Valdes, 2007) comb. nov., ‘ Trinchesia ’ mimar (Ortea and Moro, 2018) comb. nov., ‘ Trinchesia ’ miniostriata Schmekel, 1968 comb. nov., ‘ Trinchesia ’ momella Edmunds, 1970 comb. nov., Trinchesia morrowae Korshunova et al., 2019 comb. nov., ‘ Trinchesia ’ nakapila (Kim and Gosliner, 2024) comb. nov., ‘ Trinchesia ’ nigricolora (Baba, 1955) comb. nov., ‘ Trinchesia ’ ocellata Schmekel, 1966 comb. nov.,? ‘ Trinchesia’ odhneri (Er. Marcus, 1959) comb. nov., ‘ Trinchesia ’ ornata (Baba, 1937) comb. nov.,? ‘ Trinchesia ’ pallida (Eliot, 1906) comb. nov., ‘ Trinchesia ’ perca (Er. Marcus, 1958) comb. nov., ‘ Trinchesia ’ pinnifera (Baba, 1949) comb. nov., ‘ Trinchesia ’ puellula (Baba, 1955) comb. nov., ‘ Trinchesia ’ pupillae (Baba, 1961) comb. nov.,? ‘ Trinchesia ’ pumilio (Bergh, 1871) comb. nov.,? ‘ Trinchesia ’ pusilla (Bergh, 1898) comb. nov., ‘ Trinchesia ’ puti (Kim and Gosliner, 2024) comb. nov., ‘ Trinchesia ’ reflexa (Miller, 1977) comb. nov., ‘ Trinchesia ’ riosi (Hermosillo and Valdes, 2008) comb. nov., ‘ Trinchesia ’ rubrata Edmunds, 1970 comb. nov., ‘ Trinchesia ’ sibogae (Bergh, 1905) comb. nov., ‘ Trinchesia ’ signifera (Baba, 1961) comb. nov., ‘ Trinchesia ’ sororum Burn, 1964 comb. nov., ‘ Trinchesia ’ speciosa (Macnae, 1954) comb. nov., ‘ Trinchesia ’ taita Edmunds, 1970 comb. nov., ‘ Trinchesia ’ thompsoni (Garcia et al., 1991) comb. nov., ‘ Trinchesia ’ tina (Er. Marcus, 1957) comb. nov., ‘ Trinchesia ’ valentini (Eliot, 1907) comb. nov.,? ‘ Trinchesia ’ vermifera (Verrill, 1871) comb. nov., ‘ Trinchesia ’ virens (MacFarland, 1966) comb. nov., ‘ Trinchesia ’ viridiana (Burn, 1962) comb. nov., ‘ Trinchesia ’ yamasui (Hamatani, 1993) comb. nov., ‘ Trinchesia ’ willani (Cervera et al., 1992) comb. nov.,? ‘ Trinchesia ’ zelandica (Odhner, 1924) comb. nov., Zelentia Korshunova et al., 2017, reinstated, including species Zelentia amoris Korshunova and Martynov, 2022 comb. nov., Zelentia fulgens (MacFarland, 1966) comb. nov., Zelentia nepunicea Korshunova et al., 2018 comb. nov., Zelentia ninel Korshunova et al., 2017 comb. nov., Zelentia pustulata (Alder and Hancock, 1854) comb. nov., Zelentia roginskae Korshunova et al., 2018 comb. nov., and Zelentia willowsi Korshunova et al., 2018 comb. nov. For the respective diagnoses for each of the above-listed restored genera and species see also Korshunova et al. (2017 c, 2018, 2022, 2023) and Korshunova and Martynov (2022). Remarks: The family Trinchesiidae is the largest, most diverse and most species-rich family within the superfamily Fionoidea. Even the considerable number of currently recognized genera (see above) is definitely not enough to cover the extensive known diversity (Martynov 2002, Korshunova et al. 2017 c, 2022) and more genera need to be separated in a future study of the family Trinchesiidae. The family Pinufiidae, which has previously been largely neglected and rarely mentioned, was considered a family with highly uncertain placement, and never used before 1999 as a family-level taxon of suborder Aeolidacea. Instead, from the time of its first description until very recently it was invariably placed within the completely different suborder Arminacea (Marcus and Marcus 1960, Rudman 1981, 1982, Jensen 2000, Gosliner et al. 2015), or even one time near the dendronotacean family, Dotoidae (Pola and Gosliner 2010). However, Pinufius has most recently been revealed to be closely related to the genus Phestilla of Trinchesiidae (Jia et al. 2023, present study). Pinufius formed the sister-clade (PP = 1, BS = 87) to Phestilla and clustered within the Trinchesiidae group (PP = 1, BS = 84; Fig. 5 A). Therefore, accordingly ‘ Pinufiidae Marcus and Marcus, 1960 ’ is considered a subgroup of Trinchesiidae Nordsieck, 1972, e. g. as a ‘ subfamily’. The family Trinchesiidae, in turn, has been used as a valid name in a significant number of recent articles (e. g. Korshunova et al. 2017 a – c, 2018, 2019 a, 2021, 2022, Martynov et al. 2019, 2020, Hu et al. 2020 a, b, Mehrotra et al. 2020, Picton and Morrow 2023, Jia et al. 2023, and others). Therefore, this case fits within Article 35.5 of ICZN (1999, our italics): ‘ If after 1999 a name in use for a family-group taxon (e. g. for a subfamily) is found to be older than a name in prevailing usage for a taxon at higher rank in the same family-group taxon (e. g. for the family within which the older name is the name of a subfamily) the older name is not to displace the younger name’. Thus, the family Trinchesiidae Nordsieck, 1972, in prevailing usage since 2017, must be kept as a valid taxon. Surprisingly, instead of gradually continuing the further work of fine-scale genus-level differentiation within the family Trinchesiidae, whichhasbeenconsistentlyperformed (Martynov 2002, Korshunova et al. 2017 c, 2018, 2019 a, Martynov et al. 2020, present study; Figs 1, 2, 5), a strong pan-lumping bias recently led to the alleged ‘ synonymy’ of several well-supported (both morphologically and molecularly) trinchesiid genera, using a non-resolved tree full of polytomies with a highly inconsistent taxonomic discussion (Kim et al. 2024). This immediately resulted in utter chaos in WoRMS (2024) since, for example, some taxa are still assigned to the genera Catriona and Cuthona, whereas others are assigned to the pan-lumping, completely apomorphy-less ‘ Tenellia sensu latissimo ’ genus (see details in: Korshunova et al. 2022). Therefore, we have restored (see above) the incorrectly-synonymized genera, whose validity and morphological and molecular distinctness have been confirmed many times in many recent studies by several research groups (see diagnoses and discussion in: Korshunova et al. 2017 a – c, 2018, 2019 a, 2021, 2022, 2023, Martynov et al. 2019, 2020, Hu et al. 2020 a, b, Mehrotra et al. 2020, 2024) and again restrict the genus Tenellia only to the type species and a few confirmed closely related species (for details see the list above and Korshunova et al. 2022). Several more genera need to be established within the family Trinchesiidae (this is denoted by quotation marks before the genera name above), especially regarding the obviously heterogeneous and paraphyletic ‘ Trinchesia ’. Importantly, not the narrowly defined genus Trinchesia s. s., with the type species T. caerulea and a few related species, per se (Korshunova et al. 2019 a), but the subsequent lumping events (‘ Cuthona ’, ‘ Tenellia ’) that led to the current situation, when, instead of careful gradual work toward the separation of narrowly defined genera (Korshunova et al. 2017 c, 2022), we now need to again return to some basic constatation, that apart from the narrowly defined genera Zelentia, Trinchesia s. s., Diaphoreolis, Catriona, Tenellia, and Phestilla, a number of separate genera are needed to accommodate the naturally existent, highly intricate morphological and molecular diversity of the family Trinchesiidae. Respectively, many species that are listed above do not precisely match the diagnoses of genera described so far, obviously pending further revision, but again this is the result of the unfortunate persistence of profound negligibility of the fine-scale morphology and taxonomy and not an absence of understanding that, for example, the current ‘ Trinchesia ’, according to morphological and molecular data, is still not a consistent taxon. But, compared, to the super-lumped ‘ Cuthona ’ (Williams and Gosliner 1979), which turned out to contain representatives of several completely different families (see Synopsis here and above), or the pan-lumped ‘ Tenellia ’ (Kim et al. 2024), which ‘ united’ such immediately different, very easily distinguished taxa as the proper Tenellia (oral veil instead of oral tentacles, few cerata, cnidosacs present, and small size) with Phestilla s. s. (oral tentacles present, numerous cerata, cnidosacs absent, and large size), the current restriction of Trinchesiidae diversity at least to no less than 12 genera, with still significantly heterogeneous ‘ Trinchesia ’ is an important step for further revision of the family Trinchesiidae, when more genera within the former ‘ Trinchesia ’ will be separated to accommodate many fine-scale morphological characters and molecular data. For example, for some of the above listed taxa (e. g. for the genus Narraeolida, reinstated) a penial stylet was not reported in the original description, as well as other inconsistencies with the family Trinchesiidae, but these need in additional study and further confirmation. Indeed, there are a number of taxa, including undescribed hidden diversity, which have some relationship to Phestilla s. s. or Trinchesia s. s., but demonstrate both morphological differences and sufficient molecular distances, and all these fine-scale differences are pending separation at the genus-level. But along with such cases, there are still many instances, which are the results of many decades of application of the highly imprecise, profoundly polyphyletic ‘ concept’ of ‘ Cuthona ’, and which also definitely needs to be addressed. For instance, even some warm-water representatives, like ‘ Cuthona ’ fructuosa (Bergh, 1892) or ‘ Cuthona ’ destinyae Hermosillo and Valdes, 2007, according to available morphological data (Bergh 1892, Ortea et al. 2005, Hermosillo and Valdes 2007) do not belong either to ‘ Cuthona ’ or ‘ Trinchesia ’ s. l., and perhaps do not even belong to the superfamily Fionoidea, and should be considered rather as Aeolidacea incertae sedis. Further, so-called ‘ Cuthona ’ lizae Angulo-Campillo and Valdes, 2003 possesses some features similar to the distantly related family Abronicidae, and perhaps either truly belongs to Abronicidae or represents a case of a convergence within the family Trinchesiidae. These are only a few selected examples of such highly heterogeneous taxa. They, of course, are not limited only to these species, but readily show the pitfalls of the unfortunately persistent pan-lumping approach in nudibranch taxonomy. All these and many other cases, therefore, must not be a reason to synonymyze all the astonishing Trinchesiidae diversity into the diagnoses-less unmanageable taxonomic volume of ‘ Tenellia ’. At the most general scale, the persistent application of the fundamentally overlumped ‘ Cuthona ’ (and the currently overlumped ‘ Tenellia ’ as its logical continuation) for over almost half a century, has profoundly concealed both fine-scale genus-level diversity and also large-scale, family-level diversity first under ‘ Cuthona ’ and now under ‘ Tenellia ’ (see synopsis of the superfamily Fionoidea above). As one of the best examples, not just ‘ discussable’ but independent from any consideration, is the fact that when a very significant part of the diversity of many families of the superfamily Fionoidea was lumped into seemingly ‘ just single genus Cuthona ’, it was concluded ‘ that Trinchesia cannot be separated from Cuthona … ’ (Williams and Gosliner 1979: 212). Remarkably, all subsequent detailed investigations of aeolidacean systematics and phylogeny did not merely ‘ not confirm’ that statement, but profoundly abandoned it, since Trinchesia proper and the true Cuthona (instead of the pan-lumped ‘ Cuthona ’) not only are perfectly distinguished from each other morphologically (Martynov 1992 a, Korshunova et al. 2018, 2019 a), but belong to distantly related lineages according to many molecular phylogenetic analyses (summarized in the present study; Figs 1, 2, 5). The true representatives of the genus Cuthona in the family Cuthonidae proper are only so far known three valid species, type C. nana (Alder and Hancock, 1842), C. divae Er. Marcus, 1961, and C. hermitophila Martynov et al., 2015. No other species of the family Trinchesiidae or other families should be currently considered as ‘ Cuthona ’. Therefore, one more time, true Tenellia is restricted exclusively to only include the well-described valid species Tenellia adspersa (Nordmann, 1845) and Tenellia gotlandica Lundin et al., 2022, and at a maximum may include the hidden diversity of a few more species, including Tenellia pallida (Alder and Hancock, 1854) and its possible synonym Tenellia fuscata (A. Gould, 1870) (see Korshunova et al. 2022), but, crucially, other taxa of the family Trinchesiidae, must not be placed into that obviously exceedingly overlumped ‘ genus Tenellia ’ with its lack of any reliable morphological diagnostic characters and incorrect analysis of the results of the application of molecular data. Importantly, the true Tenellia is well consistent not only in paedomorphic morphology with a well-defined secondarily juvenilized oral veil (Korshunova et al. 2017 c), but highly consistent in the ecological patterns, being predominantly associated with brackish or lowered salinity waters (although able to tolerate higher salinity), such as estuaria and seas with low salinity, such as, for example, the Black Sea, the very type locality of T. adspersa (Korshunova et al. 2022). Remarkably, the true Tenellia, is the only taxon that is able to penetrate quite far along the upper Thames estuary (Thompson and Brown 1984), Caspian Sea (Antsulevitch and Starobogatov 1990), and the most brackish parts of both of the Azov Sea (Roginskaya 1970, Martynov 2006 b) and Baltic Sea, including Finland (Evertsen et al. 2004) and Russia (our own data). Furthermore, from such peculiar brackish and low salinity habitats, Tenellia adspersa and closely related species were able to widely distribute over the similar habitats in the Northern Hemisphere, using anthropogenic transportation, over 10 000 km, sometimes far from the type locality for example in Japan, where it is immediately recognized exactly as true Tenellia and explicitly considered as an alien (invasive) species (Kashio 2018, Kashio and Hamatani 2018), not as some other Trinchesiidae, and also commonly occurs in some peculiar habitats like port harbours. The specimens from Osaka Bay (Kashio 2018) were studied in Korshunova et al. (2022) and showed strong genetic identity with the T. adspersa from the type locality in the Black Sea. This is the best proof that true Tenellia despite the presence of other described or not yet described genera within Trinchesiidae with partly paedomorphic, independently gained morphology is an immediately recognizable taxon. To ‘ synonymyze’ true Tenellia with other diverse genera of the family Trinchesiidae would be similar highly dismissive action as to synonymyze the genus Pan Oken, 1816 with the genus Homo Linne, 1758, using the priority rule, the misleading designation of ‘ overall similar morphology’, and apparently small molecular genetic distances (Martynov and Korshunova 2022).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA1FFC0FEB6FA09FD2FFD81.taxon	description	(Figs 1, 3) urn: lsid: zoobank. org: act: 5 C 7 C 83 F 9 - 3290 - 4 C 80 - B 0 F 0 - 2 C 856349 A 112 Etymology: From Japanese kiku (キク), chrysanthemum, to denote the external similarity of this beautiful new species to the flower that is iconic in Japanese culture. Holotype: KM 1077, L = 13 mm (live), Japan, Okinawa, Sakimotobu beach, 3 m depth, 31 October 2021, coll. Kaoru Imagawa. Description External morphology (Fig. 3 A – D) Body elongate. Rhinophores similar in size to oral tentacles, smooth. Cerata notably long, thin, mostly finger-shaped, some partly fusiform, placed on several distinctly elongated elevations with ceratal clusters along dorsal edges. Apices of cerata pointed, with elongated cnidosacs. Distinct notal edge absent. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic toward acleioproctic position on right side below second large ceratal cluster. Reproductive openings lateral, below first anterior cluster of cerata. Colour (Fig. 3 C, D) General colour translucent dark orange, with thin purple middorsal line. Oral tentacles irregularly covered in purple pigment nearly half its length, basal half of oral tentacles and further toward tip covered with irregular white spots. Rhinophores covered with similar irregular white spots, apical part unevenly purple. Cerata variegated due to encrustation of white specks and small spots, dark pinkish to light brownish branches of the digestive gland show through. Subapical purple rings on cerata, apices yellowish. Jaws (Fig. 3 E, F) Jaws broadly triangular, masticatory borders with unique elaborate long denticles in clusters of up to about 70. Radula (Fig. 3 G, H) Radula formula 30 × 0.1.0. Central tooth with up to at least eight distinct denticles. Central cusp smooth, widened in the middle and distinctly narrowed toward the tip; no small denticles at the base of the posterior and middle teeth. No lateral teeth. Reproductive system (Fig. 3 I, J) Ampulla voluminous, bent. Prostate distinct, thick. Vas deferens short, penial sheath oval, conical penis armed with hollow stylet. Two proximal receptaculum seminis. Ecology: Shallow water environment. Distribution: So far known from Okinawa, Japan, potentially may be found in other tropical waters. Remarks: The new species Unidentia kiku sp. nov. (Fig. 1) clustered together with Unidentia aliciae, Unidentia sp., Unidentia nihonrossija, and U. sandramillenae, constituting a highly supported clade (PP = 1, BS = 100) according to the molecular phylogenetic data of the present study. The COI minimal uncorrected p - distances between the U. kiku sp. nov. clade and Unidentia aliciae, Unidentia sp., Unidentia nihonrossija, and U. sandramillenae clades are 15.5 %, 17.0 %, 16.0 %, and 15.5 %, respectively. Externally, U. kiku sp. nov. immediately differs from U. sandramillenae by its translucent dark orange ground and variegated (Fig. 3) and not whitish or light purple ground colour and generally more uniform coloration. Internally, the general pattern of the radular teeth of U. sandramillenae readily differs from Unidentia kiku sp. nov. by having a more ‘ pectinate’ appearance of the central teeth [compare U. sandramillenae from fig. 43 H, I in Korshunova et al. (2017 a) and U. kiku sp. nov. from Fig. 3 G, H, in the present study]. Unidentia aliciae Korshunova et al. 2019 (Fig. 2), distantly related according to the present molecular phylogenetic analysis, well differs from U. kiku sp. nov. by its creamy-yellowish ground coloration and details of the reproductive system, with considerably larger proximal receptaculum seminis (Korshunova et al. 2019 b). Finally, the only described species of Unidentia from Japan so far, U. nihonrossija Korshunova et al., 2017 (but from the Pacific side of the main Japanese Island Honshu) immediately differs from U. kiku sp. nov. by its whitish background colour and reddish-orange, largely non-variegated coloration and details of its radular patterns (see: Korshunova et al. 2017 a: fig. 42 and present study, Fig. 3), and significant molecular phylogenetic distance (Fig. 2). Unidentia angelvaldesi Millen and Hermosillo, 2012, with no molecular data available, readily differs morphologically from U. kiku sp. nov. by the inclusion of forms with more uniform reddish coloration and the presence of only a single receptaculum seminis [compare Millen and Hermosillo (2012: fig. 7 F) and the present study, Fig. 3].	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA1FFC1FF37FCAFFDFEFAFC.taxon	materials_examined	Type species: Unidentia angelvaldesi Millen and Hermosillo 2012. Diagnosis: Body narrow. Notal edge completely reduced. Cerata on distinct elongate elevations. Rhinophores smooth. Anterior foot corners present. Anus mixed (pleuroproctic in a higher acleioproctic position) or pleuroproctic. Central teeth with broad to narrow non-compressed cusp and distinct denticles. Lateral teeth absent. Proximal double or, rarely, single receptaculum seminis. Distal receptaculum seminis absent. Moderately long to short vas deferens with rapidly widened distinct prostatic part. Accessory gland absent. Penis conical, with relatively short hollow stylet. Species included: Unidentia aliciae Korshunova et al., 2019, U. angelvaldesi Millen and Hermosillo, 2012, U. nihonrossija Korshunova et al., 2017, Unidentia kiku sp. nov., and U. sandramillenae Korshunova et al., 2017.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFACFFC1FC8CFCCCFE20FC9A.taxon	description	(Figs 1 – 4; Table 4) ‘ Genus Flabellina sensu latissimo ’ Gosliner 2010: 630.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFACFFC1FC8CFCCCFE20FC9A.taxon	diagnosis	Diagnosis: Body moderate to narrow. Notal edge completely reduced. Cerata on indistinct elevations or low stalks, numerous per row. Ceratal rows branched to simple. Rhinophores smooth. Anus pleuroproctic or mixed in a higher acleioproctic position. Jaws with masticatory edges bear a single or several irregular to distinctly sharpened, elongate denticles. Radula formula 0.1.0. Central teeth with non-compressed cusp. Distal and proximal receptaculum seminis or only proximal receptaculum (single or double). Vas deferens moderately long to short, prostate distinct. Supplementary gland absent. Accessory gland absent or present (not confirmed). Massive external permanent penial collar absent. Penis internal, not considerably widened, armed or unarmed. Genera included: Pacifia Korshunova et al., 2017, Unidentia Millen and Hermosillo, 2012, and Phetia gen. nov. Remarks: The validity and distinctness of the family Unidentiidae was confirmed for the first time using molecular phylogenetic data in Korshunova et al. (2017 a). Prior to this, members of that highly distinctive family had been considered under the pan-lumping genus name ‘ Flabellina ’ (Gosliner 2010) despite subsequent separation using only morphological data (Millen and Hermosillo 2012). Until the molecular phylogeny presented by Korshunova et al. (2017 a), the status of the family Unidentiidae was fundamentally uncertain. In the present study, we further resolve the ‘ Flabellina ’ overlumped assemblage previously assessed in major details (Korshunova et al. 2017 a, b), and the still not completely resolved ‘ Piseinotecus ’ sensu latissimo pan-lumping grouping, and we present robust evidence that the so-called ‘ Piseinotecus ’ soussi from the Mediterranean (Tamsouri et al. 2014) in reality represents a member of a new genus from the family Unidentiidae (see Results, Figs 1, 2, 4). By this, we further significantly undermine the ‘ integrity’ of the so-called ‘ Piseinotecidae’, which still appear as a highly ambiguous family, because the new genus is robustly placed in a completely different superfamily Unidentioidea (Figs 1, 2, 4). According to the present study, another alleged ‘ Piseinotecus ’ or ‘ Flabellina ’ (Gosliner et al. 2015, 2018) enigmatic taxon, distantly related to Unidentioidea, is robustly placed within a completely different superfamily Flabellinopsoidea, as a new family Hantazuidae fam. nov., with the inclusion of the new genus Hantazuia gen. nov. and three new species (see Synopsis below; Figs 1, 2). Thus, following the evident, robust demonstration of the profound polyphyly of the pan-lumping genus ‘ Flabellina ’ sensu Gosliner and Griffiths (1981) (see: Korshunova et al. 2017 a, b), in the present study we have significantly expanded the diversity of the family Unidentiidae, and further demonstrate the similar deep polyphyly of the putative family ‘ Piseinotecidae’, whose members have been re-arranged into at least three families of completely different, distantly related superfamilies Flabellinopsoidea, Flabellinoidea and Unidentioidea (Fig. 2). The genus-level structure of the family Unidentiidae (see Synopsis below; Figs 1 – 4) well reflects underlying evolutionary pathways and is consistent with the morphological data and phylogeographic patterns. Particularly, the ‘ largest’ (five described species, including one new species in the present study, plus additional hidden diversity; Fig. 3) genus so far, Unidentia, is characterized by the presence of a relatively short penial stylet and inhabits exclusively the true tropical waters of the Indo-West and Eastern Pacific (Millen and Hermosillo 2012, Korshunova et al. 2017 a, 2019 b). The genus Pacifia is characterized by an unarmed penis, and inhabits boreal to subtropical waters of the NE Pacific. The new genus Phetia gen nov. is characterized by a long sabre-shaped penial stylet and known so far exclusively from subtropical Mediterranean basin.	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
03EF87FEFFA6FFC6FC62FE93FAE8F9D8.taxon	description	(Figs 1, 2; Table 4) Martynov et al. 2020: 14. Diagnosis: Body wide. Notal edge completely reduced. Cerata not stalked, in few continuous rows, no more than five anterior rows (fifth row rudimentary, if present). Rhinophores smooth. Anus acleioproctic. Masticatory edges of jaws commonly bear single row of compound denticles. Radula formula 0.1.0. Central radular teeth pectinate, with strong non-compressed cusp and additional denticles. Distal receptaculum seminis present. Vas deferens long, prostate indistinct, narrow tubular. Supplementary gland present, inserts to penis. Massive external permanent penial collar absent. Penis internal, conical, unarmed. Genera included: Xenocratena Odhner, 1940. Remarks: The family Xenocratenidae, aside from being phylogenetically sister to Murmaniidae (Figs 1, 2), otherwise fundamentally differs from it and evidently displays paedomorphic reduced features in the presence of a small, non-massive body with a completely reduced notal edge, cerata organized in a few rows, and an acleioproctic anus (see: Martynov et al. 2020; Synopsis above). The family Xenocratenidae provides an important insight for the current persistent attempts to lump both fine-scale and large-scale diversity into highly heterogeneous and para- and polyphyletic ‘ Cuthona’ and ‘ Tenellia’ (see below), because since the original description of the genus Xenocratena (Odhner 1940), it was commonly listed either as a doubtful taxon, or as a synonym of ‘ Cuthona’ (Miller 1977, Williams and Gosliner 1979). However, after the first rediscovery of that amazing taxon less than 10 years ago, it has been shown that Xenocratena and Xenocratenidae belong to a profoundly different lineage compared to both families Cuthonidae and Trinchesiidae (Martynov et al. 2020; present study) (Figs 1, 2). Furthermore, because Xenocratena not only has a similar name to one of the most enigmatic metazoan Xenoturbella, but inhabits fundamentally same geographic location, depths, and soft substrates, the conclusions of the paedomorphic reduction of Xenocratena due to inhabiting soft marine sediments, were also applied to the potential origin of Xenoturbella (Martynov et al. 2020), and these conclusions were confirmed most recently by a detailed analysis of the Xenoturbella genome (Schiffer et al. 2024).	en	Korshunova, Tatiana, Fletcher, Karin, Martynov, Alexander (2025): The endless forms are the most differentiated-how taxonomic pseudo-optimization masked natural diversity and evolution: the nudibranch case. Zoological Journal of the Linnean Society 204 (4), DOI: 10.1093/zoolinnean/zlaf057, URL: https://doi.org/10.1093/zoolinnean/zlaf057
