Pseudobornella Baba, 1932

Korshunova, Tatiana, Bakken, Torkild, GrØtan, Viktor V., Johnson, Kjetil B., Lundin, Kennet & Martynov, Alexander, 2021, A synoptic review of the family Dendronotidae (Mollusca: Nudibranchia): a multilevel organismal diversity approach, Contributions to Zoology 90 (1), pp. 93-153 : 133-134

Genus Pseudobornella Baba, 1932

Type species. P. orientalis Baba, 1932 (fig. 2)

Diagnosis. Dorsolateral appendages without distinct (or with few very short) tertiary branches. One of the rhinophoral stalk appendagesfrom both sides is extremely long, usually exceeding body length. Oral veil with long simple unbranched appendages. Radula with very small number of lateral teeth (presently knowntobe no morethantwo rows of lateral teeth). Central teeth with protruding cusp distinctly separate from lateral denticles. Prostate represents by narrow tube, without alveols and disk. Copulative organ partly flattened and with a widened subcircular apical part.

Remarks. The genus Pseudobornella differs from both Dendronotus and Cabangus gen. nov. by a unique combination of external and internal characters.These characters includea very long appendage of the rhinophoral sheath, absence of distinct tertiary branches of the dorsolateral appendages, resultinginthegeneralappearance of dorsolateralappendagesof Pseudobornella as ctenidium-like. Instead, all species of the genus Dendronotus possess well-defined tertiary branchesonthedorsolateralappendages,andno species has suchaexceedingly longappendages of the rhinophoral sheaths. There is a deep-sea species, Dendronotus claugei (see above), for which unbranched dorsolateralappendagesare reported, but this species is only known from a single specimen and needs further studies. According to the present phylogeny D. claugei may represent a separate genus, but more data are needed to support this. Furthermore, so far no single species of the genus Dendronotus and Cabangus gen. nov. have smooth unbranched appendages in the oral veil, whereas numerous reported Pseudobornella specimens invariably show strong unbranched appendages of the oral veil. Ultimately, the radular pattern of the genus Pseudobornella differs from that in the adult stage of species of Dendronotus and Cabangus gen. nov. by a very small number of lateral teeth (so farreportedno morethan two). Adult specimens of the genera Dendronotus and Cabangus gen. nov. possess at least eight lateral teeth, and only very rarely in poorly known deep-sea lineages, the number of the lateral teeth rows can reach six in number. The tropical C. noahi was reported to have only four rows of lateral teeth, but only a single juvenile specimen is known ( Pola & Stout, 2008). All investigated species of the genus Dendronotus showed thepresence of 1–3 rows oflateral teeth during the early stages of their ontogeny (e.g., Martynov et al., 2020a), while only in the genus Pseudobornella such feature became apparent in adults stage. Furthermore, the shape of the central teeth of Pseudobornella is also different from that in any adult Dendronotus and Cabangus gen. nov. species by the presence of a strongly protruding central cusp on the central teeth, which is distinctly separated from the lateral denticles.

ASEMimageoftheradulaof P.orientalis from the Sea of Japan was presented in Martynov et al. (2015a: 60, fig. 5G). Radular characters coupled with the molecular data (including presenting for the first time data on COI gene for the type species Pseudobornella orientalis , figs 1, 2) show that the genus Pseudobornella represents an early offshoot of the family Dendronotidae . This evolution was fuelled by the paedomorphic reduction of the lateral teeth and juvenilization of the central teeth (for criteria of paedomorphosis ( Korshunova et al., 2020a; Martynov et al., 2020b). Aprevious morphological cladistic study ( Pola et al., 2009) placed the genus Pseudobornella outside the family Dendronotidae , thus highligthing the morphological peculiarities of this genus as inconsistent with those of other dendronotid genera. However, a solely molecular study suggested to synonymize Pseudobornella with Dendronotus ( Pola & Gosliner, 2010) . We confirm here the validity of the genus Pseudobornella Baba, 1932 using integrative evidences. Specimens of the type species Pseudobornella orientalis from the Sea of Japan (fig. 2) in the present study matched morphologically well with those in the original description of P. orientalis ( Baba, 1932) , including the characteristic small chocolate-brown spots and yellow lines on the dorsal side, and the shape of the radular teeth.

Species composition. This presently monospecific genus only contains P.orientalis Baba, 1932 .