Unidentiidae Millen and Hermosillo, 2012

Family Unidentiidae Millen and Hermosillo, 2012 View in CoL

( Figs 1–4; Table 4)

‘Genus Flabellina sensu latissimo ’ Gosliner 2010: 630 .

Family Unidentiidae Millen and Hermosillo 2012: 155 View in CoL .

Family Unidentiidae View in CoL validity confirmed, Korshunova et al. 2017a: 54.

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. (2017a). 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. (2017a), 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. 2017a, 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. 2017a, 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. 2017a, 2019b). 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.