Unidentiidae Millen & Hermosillo, 2012

Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017, Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda), ZooKeys 717, pp. 1-139 : 49-51

Family Unidentiidae Millen & Hermosillo, 2012

Diagnosis.

Body narrow. Notum fully reduced. Cerata in separate clusters, on distinct elongated elevations. Rhinophores smooth. Anus pleuroproctic or mixed (pleuroproctic in higher acleiproctic position). Distinct oral glands present. Radula formula 0.1.0. Rachidian teeth with non-compressed cusp. Lateral teeth always absent. Number and position of receptaculum seminis variable: two separate ones, or double or single proximal ones. Vas deferens moderately long, with distinct prostate. External permanent penial collar absent. Adjacent penial gland present or absent. Penis conical, armed or unarmed, always internal.

Genera included.

Pacifia gen. n., Unidentia Millen & Hermosillo, 2012.

Remarks.

This is a very interesting case which shows the polyphyletic nature of the traditional Flabellinidae . In 2010 a species with uniseriate radula and unusual supplementary penial gland was added to the traditional genus Flabellina ( Gosliner 2010) despite the fact that the outlined characters directly contradict such a decision. The present molecular phylogenetic analysis fully confirms this species to be extremely disparate from the majority of Flabellinidae s. str. as suggested by its morphology. Flabellina goddardi and a new closely related species from the Pacific coast of Japan (see below) were clustered together in the same clade which was placed basally to the family Facelinidae and not clustering with any other Flabellinidae (Figs 1, 2). Importantly, this taxon is invariably placed basally to Facelinidae in any variants of the obtained trees and not nested within the family Flabellinidae s. str. as was suggested by Gosliner (2010: 630). Remarkably, two other new species of the genus Unidentia from Japan and from Indonesia also possess a uniserial radula and pleuroproctic anus in a higher acleioproctic position. This challenging taxon, with a new genus and two species, is confirmed for the first time in the present study as belonging to the family Unidentiidae Millen & Hermosillo, 2012.

Currently, many researchers are actively debating phylogenetic relationships and higher taxonomy of one of the most diverse nudibranch groups, Aeolidacea (e.g., Carmona et al. 2013; Padula et al. 2014; Kienberger et al. 2016; Korshunova et al. 2017a; Korshunova et al. 2017c). However, until recently no molecular analysis of aeolidacean nudibranchs has included the family Unidentiidae . When Gosliner (2010) described F. goddardi he only mentioned a preliminary molecular phylogeny, but no trees or molecular analyses have been presented since his publication. In addition, Gosliner (2010: 630) has highlighted that his data "strongly suggest that F. goddardi , despite having a uniseriate radula, is most closely related to other species of Flabellina ". However, the first molecular analysis of this group presented here has clearly and robustly shown that the family Unidentiidae (including the newly described Pacifia amica gen. n. et sp. n. and Pacifia goddardi comb. n.) is not related to any real Flabellina , but instead to the family Facelinidae . Since all members of the Facelinidae have a uniserial radula (i.e., as in Unidentiidae ) in strong contrast to a triserial radula in traditional Flabellinidae , the phylogenetic relationship of Unidentiidae to Facelinidae (Fig. 1) uncovered in the present study is in much greater agreement with the morphological data on radula, thus confirming the general integrative agenda for taxonomy ( Dayrat 2005; Korshunova et al. 2017b).

The morphological cladistic analysis ( Millen and Hermosillo 2012) also placed the uniserial family Unidentiidae as a basal group to the triserial Flabellinidae , but included including some uniserial groups like Piseinotecus and Babakina . However, most recently ( Furfaro et al. 2017) it was shown, in remarkable agreement with our molecular phylogenetic study, that some species placed in Piseinotecus actually possess a triserial radula and are closely related to the true Flabellinidae , and that delicate lateral teeth were previously simply unrecognised. Since on the morphological cladogram the genus Piseinotecus was clustered basally to the also uniserial genus Babakina (the family Babakinidae ) it may thus not reflect the real phylogenetic placement. In our phylogenetic analysis, the genus Babakina is not related to any Flabellinidae or Unidentiidae , but instead placed basally to the family Aeolidiidae (Fig. 1).

Thus, this first molecular data and molecular analysis of the family Unidentiidae clearly shows that previous morphological estimations of the F. goddardi as a proper flabellinid ( Gosliner 2010) (despite the uniserial radula) or a group closely related to the traditional family Flabellinidae ( Millen and Hermosillo 2012) were incorrect. However, Millen and Hermosillo (2012) prophetically separated Unidentia into an independent family that is now fully confirmed by our molecular analysis. Our new data also confirm the reliability of the detailed morphological analysis on an integrative basis ( Korshunova et al. 2017a) since striking differences of the uniserial F. goddardi and Unidentia with the triserial traditional Flabellinidae , previously considered as just an independent case of reduction of lateral teeth, (e.g., according to the cladogram in Millen and Hermosillo 2012) is actually an indication of phylogenetic relationship with the uniserial traditional Facelinidae . The retaining of a pleuroproctic anus, or pleuroproctic in a higher acleioproctic position in Unidentiidae , can be considered therefore as a plesiomorphic feature (see Korshunova et al. 2017c for a discussion of the plesiomorphic pleuroproctic position in Nudibranchia ).

The present new findings and the first molecular phylogenetic analysis involving members of the family Unidentiidae thus not only has particular taxonomic importance but also makes important contributions for the understanding of the phylogeny of the whole Nudibranchia group and for the general discussion about the plausibility of using morphological data for phylogenetic analysis and high-level systematics.

In the combined phylogenetic tree, all Unidentiidae species clustered in a highly supported clade together (PP = 1, BS = 98) that is dramatically separated from the Flabellinidae clade. All Unidentia species clustered together (PP = 1, BS = 100) in a maximum-supported clade that is sister to the maximum-supported (PP = 1, BS = 100) clade with the species of Pacifia gen. n.

The family Unidentiidae originally was incorrectly spelled as Unidentiidae ( Millen and Hermosillo 2012). The name is based on Unidentia with the stem therefore being Unidenti-, so the original name Unidentiidae should be corrected to Unidentiidae with the same author and date ( ICZN 1999, article 29.3).