Dendronotus gracilis Baba, 1949

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 : 120-121

Dendronotus gracilis Baba, 1949

Dendronotus gracilis Baba, 1949: 167 , Pl. 35, Fig. 127, text-fig. 109; Robilliard, 1970: 461–462; Nakano, 2018: 385.

Diagnosis (original description). Body narrow. Four pairs of branched dorsolateral appendages. Four veil appendages. Five to six processeses of the rhinophoral stalks. Rhinophores with 18 lamellae. Basal colour bluish-white, with numerous scattered yellow spots, various processes opaque white. Masticatory processes of jaws with denticles. Radula with upto 41 rows of teeth. Central tooth with upto 20 small denticles without furrows, rarely completely smooth. Up to eight lateral teeth with up to nine denticles. Reproductive system unknown. Body length 25 mm (living, original description).

Distribution. Japan, Pacific side of Honshu, Japan.

Bathymetry. 160 mdepth (original description).

Remarks. This species is insufficiently known. Information on the internal morphology of specimens from the type locality is restricted to the original description ( Baba, 1949). Additional data in Pola and Stout (2008) referring to D. gracilis specimens are from considerably remote locations off the tropical island of Okinawa, whereas the type locality of D. gracilis is in the temperate Sagami Bay. Their study lacks molecular data and may represent a separate species. The Okinawan specimen indicated in Pola and Stout (2008) has eight pairs of dorsolateral processes, six processess of the oral veil, and 12 rhinophoral lamellae, whereas according to the original description in Baba (1949) there are four pairs of dorsolateral processes, four processesses of the oral veil, and 18 rhinophoral lamellae, respectively. Taking into consideration that details of colourpatterms between the original description of D. gracilis and Okinawan specimens are also different as indicated by Pola and Stout (2008: 65), we cannot confirm the conspecificity of the Okinawan specimens with the original D.gracilis , even if weconsider the potentially cooler waters in Okinawa at 69 mdepth and that only a few specimens were involved in the comparison. Furthermore, Pola and Stout (2008) considered specimens from New Zealand as belonging to D. gracilis as well, which also show differences in colouration. However, in the light of a modern emerging paradigm of multilevel organismal diversity that challenges the previously concept of widely claimed polytypic species with broad ranges in favour of considerably smaller, often geographically restricted species, a potential presence of true D. gracilis in New Zealand can only be the result of an anthropogenic transportation, which is hard to explain in this case and needs verification.