Dendronotus kurilensis, Ekimova & Valdés & Stanovova & Mikhlina & Antokhina & Neretina & Chichvarkhina & Schepetov, 2021

Ekimova, Irina, Valdés, Ángel, Stanovova, Maria, Mikhlina, Anna, Antokhina, Tatiana, Neretina, Tatiana, Chichvarkhina, Olga & Schepetov, Dimitry, 2021, Connected across the ocean: taxonomy and biogeography of deep-water Nudibranchia from the Northwest Pacific reveal trans-Pacific links and two undescribed species, Organisms Diversity & Evolution (New York, N. Y.) 21 (4), pp. 753-782 : 770-772

Dendronotus kurilensis sp. nov.

urn:lsid:zoobank.org:act:F8048B84-91A5-4717-9A56-74D9BF185BCF

( Figs. 3D and 12 )

Type material: Holotype: MIMB 42237 , Sea of Okhotsk , Urup Is., 46°15′9″ N, 150°15′4″ E, depth 450–460 m, July 05, 2019, R / V Akademik Oparin . Paratypes: MIMB 42236 , Sea of Okhotsk , Urup Is., 46°16′7″ N 150°16′5″ E, depth 227– 210 m, August 18, 2019 . MIMB 42235 , Sea of Okhotsk , Urup Is., 46°16′7″ N 150°16′5″ E, depth 227– 210 m, August 18, 2019, 4 specimens . MIMB 42238 , Sea of Okhotsk , Iturup Is., 45°44′6″ N, 148°34′0″ E, depth 264–270 m, July 07, 2019 , R / V Akademik Oparin, 1 specimen .

Etymology: After “Kuril Islands”, the type locality of this species.

Type locality: Sea of Okhotsk , Urup Is., 46°15′9″ N, 150°15′4″ E, depth 450–460 m.

External morphology ( Fig. 12A–E ): Body up to 30 mm long, laterally compressed, elongate. Oral veil large, with up to six simple conical appendages. Four branched rhinophoral sheath appendages of same size, lateral papilla absent, rhinophores perfoliated with up to 12 lamellae. Up to seven pairs of stout dorsolateral appendages with simple secondary branching. Anal opening on right side of body about midway between first and second pairs of dorsolateral processes. Reproductive openings located laterally near first pair of dorsolateral processes on right side.

Color ( Fig. 12A–E ): Uniform milky pink to peach. Anterior part of body, dorsolateral appendages and surface between them with bright orange pigmentation.

Anatomy: Jaws elongated plates with strong dorsal process and slightly curved masticatory border ( Fig. 12F ), bearing row of denticles and two rows of smaller denticles underneath ( Fig. 12G, E ). Radular formula in studied specimens 29 × 8–10.1.8–10. Rachidian tooth with up to 10 large denticles on each side of reduced cusp, with deep furrows ( Fig. 12I, K ). Lateral teeth slightly curved with sharp cusp and up to 5 denticles ( Fig. 12L ). Inner- and outermost laterals subulate. Reproductive system triaulic ( Fig. 3D ). Ampulla relatively small, convoluted. Prostate with up to 10 alveoli. Distal vas deferens winding, moderate in length, slightly narrowing into curved ejaculatory portion. Wide vagina gradually narrowing into muscular bursa copulatrix, receptaculum seminis small, indistinct.

Molecular data: On our phylogenetic reconstruction based on 4 markers (COI, 16S, H3 and 28S), Dendronotus kurilensis sp. nov. specimens are clustered together into a single highly supported group (PP= 1; ML = 96) ( Fig. 9A ). This clade is sister to NE Pacific Dendronotus claguei Valdés, Lundsten & N. G. Wilson, 2018 (LACM3554) (PP= 1; ML = 87). Although only H3 data are available for the latter species, it differs from D. kurilensis sp. nov. by four substitutions. Since H3 is a slowly evolving molecular marker, which is commonly identical in sister Dendronotus species ( Ekimova et al., 2015, 2016a, b, 2019), the four substitutions seem to be enough molecular divergence to support D. kurilensis sp. nov. distinctness at molecular level. The clade including D. kurilensis sp. nov. and D. claguei is sister to the Dendronotus robustus - Dendronotus patricki clade in the phylogenetic tree.

Biology: This species was found in two localities represented by similar gravel sand communities, with numerous sponges and hydrozoans, annelids, and echinoderms.

Distribution: Known only from the southern Kuril Islands.

Remarks: This species is a representative of a recently discovered clade of deep-sea dendronotids with narrow body and the Dendronotus frondosus radular type ( Ekimova et al., 2019; Valdés et al., 2018). It shares many morphological similarities with another member of this group, Dendronotus claguei including body shape, absence of lateral rhinophoral sheath papillae, radular configuration, and details of the reproductive system. However, the two species differ substantially in external appearance: D. claguei possess up to six pairs of very simple conical appendages with almost no branching, asymmetric rhinophoral sheath appendages, longer oral veil appendages, while only four pairs of secondary branched appendages were found in D. kurilensis sp. nov., and rhinophoral sheath appendages are equal in this species. Finally, D. claguei coloration is transparent white instead of the milky-pink to peach coloration of D. kurilensis sp. nov. The two species are also distinct genetically, with 4 substitutions in H3 marker. Other species of the family Dendronotidae do not possess similar combination of external and internal characters. The sister clade of this group is the “ robustus ” species group, represented by wide-bodied species with unique radular morphology ( Ekimova et al., 2019; Korshunova et al., 2020b).

Superfamily Fionoidea Gray, 1857

Family Fionidae Gray, 1857 s.l.

Genus Cuthona Alder & Hancock, 1855

Cuthona sp.

( Fig. 13 )

Material studied: MIMB 42232 , Sea of Okhotsk , Shiashkotan Is., 48°48′3″ N 154°17′7″ E, depth 285–304 m, August 12, 2019, 1 specimen .

42235d, denticulation of masticatory border. F, MIMB 42235b, posterior radular portion. G, MIMB 42235b, rachidian tooth. G, MIMB 42235b, lateral teeth. Scale bars: A–E, 5 mm; F, 200 µm; G, H, 25 µm; I, 50 µm; K, L, 20 µm. Living photos by Anastassya Maiorova

External morphology ( Fig. 13A ): Body 6 mm in length, elongate, relatively wide, narrowing posteriorly. Numerous elongate, dorsolateral cerata in dense indistinct rows. Oral tentacles absent, probably due to traumatic removal during sampling. Rhinophores stout, smooth. Reproductive opening placed laterally on anterior body part. Anal opening lateral, posterior to pericardium.

Color ( Fig. 13A ): Homogenous milky-white. Anterior digestive organs visible through skin as pink mass. Cnidosac areas marked with opaque white dots.

Anatomy: Buccal mass large. Jaws triangular elongate plates, masticatory border with single row of denticles. Radula uniseriate ( Fig. 13B, C ), 18 rows. Rachidian tooth broad, with non-compressed large conical cusp and 5–6 denticles on each side.

Animal was not fully mature, and its poor preservation state did not allow to study the reproductive system in details.

Molecular data ( Fig. 14A, B ): According to the molecular phylogenetic analysis of three markers (COI, 16S, H3) our specimen form a singleton, which is sister to Cuthona nana (Alder & Hancock, 1842) , C. hermitophila Martynov, Sanamyan & Korshunova, 2015 and C. divae (Er. Marcus, 1961) clades and Bohuslania matsmichaeli Korshunova, Lundin, Malmberg, Picton & Martynov, 2018 (PP= 1; ML =100) ( Fig. 14B ).

Biology: This species was found in a species-rich community of gravel sand, including numerous echinoderms, annelids, sponges, and hydrozoans.

Distribution: Known only from the Northern Kuril Islands, deep-water area near Shiashkotan Is.

Remarks: This specimen was severely damaged during collection, which does not allow us to provide a full description of its external and internal characters. This also complicates a comprehensive comparison of morphological characters across our specimen and known Cuthona species. Nevertheless, Cuthona sp. fits well to the diagnosis of the genus Cuthona : wide body, cerata in rows non-elevated and numerous, rhinophores smooth, rachidian tooth with strong cusp ( Fig. 13 ). The coloration and overall appearance resemble the morphology of Cuthona methana Valdés, Lundsten & N. G. Wilson, 2018 , which was described recently from methane seeps in deep sea off California. The rachidian tooth of C. methana also possesses a strong cusp but has less denticles. Therefore, we suggest our Cuthona sp. may represent a sister species to C. methana . Unfortunately, no molecular data is available for the latter species.

Figures

Fig.3 Reproductive system. A, Bathydoris antoni sp. nov., general view. B, Bathydoris antoni sp. nov., male part and female gland mass partly removed. C, Dendronotus patricki, MIMB 42240. D, Dendronotus kurilensis sp. nov., paratype MIMB 42238. Abbreviations:

Fig. 12 Dendronotus kurilensis sp. nov., external morphology and SEM micrographs of internal morphology. A, holotype MIMB 42237, dorsal view. B, MIMB 42237, lateral view from left. C, holotype MIMB 42237, lateral view from right. D, paratypes MIMB 42235. E, paratype MIMB 42238. C, MIMB 42235b, right jaw plate. D, MIMB 42235b, denticulation of masticatory border. E, MIMB

Fig.9 Results of molecular analysis of genus Dendronotus. A, molecular phylogenetic hypothesis, maximum likelihood, concatenated dataset of four markers (COI+16S+H3+28S), species-level clades and outgroups are collapsed to a single branch, except target species. Numbers above branches indicate posterior probabilities from Bayesian inference, numbers below branches, bootstrap support from maximum likelihood. B, Dendronotus dalli, COI haplotype network produced with TCS method in PopART. Colors of circles refer

Fig. 13 Cuthona sp., MIMB 42232, external morphology and SEM micrographs of internal morphology. A, living specimen. B, radula. C, rachidian teeth. Scale bars: A, 5 mm; B, 100 µm; C, 20 µm. Living photo by Anastassya Maiorova

Fig. 14 Results of molecular analysis of different aeolid groups. A, genus Cuthona, COI haplotype network produced with TCS method in PopART. Colors of circles refer to the geographic origin of each haplotype. The relative size of circles is proportional to the number of sequences of that same haplotype. B, molecular phylogenetic hypothesis of genus Cuthona, maximum likelihood, concatenated dataset of three markers (COI+16S+H3), species-level clades and outgroups are collapsed to a single branch, except Cuthona and Bohuslania species. Numbers above branches indicate posterior probabilities from Bayesian inference, numbers below branches, bootstrap support from maximum likelihood. C, molecular phylogenetic