Hantazuia yugoikedai, Korshunova & Fletcher & Martynov, 2025

Hantazuia yugoikedai sp.nov.

( Figs 1, 7)

urn:lsid:zoobank.org:act:

Etymology: In honour of citizen scientist Yugo Ikeda (池田雄 吾) who in the waters of Jogāshima Island (城ケ 島), Japan, observed nudibranchs for many years and made a very important contribution by collecting material for the present study.

Holotype: KM1044 , L = 12 mm (live), north-western Pacific , Japan, Honshu, Jogāshima Island waters, stones, 10–20 m depth, 30 August 2023, coll. Yugo Ikeda.

Paratype: KM1070 , L = 12 mm (live), north-western Pacific , Japan, Honshu, Jogāshima Island waters, stones, 10–20 m depth, 12 August 2023, coll. Yugo Ikeda.

Paratype: KM1071 , L = 15 mm (live), north-western Pacific , Japan, Honshu, Jogāshima Island waters, stones, 10–20 m depth, 20 July 2023, coll. Yugo Ikeda.

Description

External morphology ( Fig. 7A–D, L, S) Body narrow. Foot and tail narrow, anterior foot corners moderate in length. Rhinophores similar in length to oral tentacles, smooth. Dorsal cerata finger-shaped to fusiform, forming up to about 20–25 small curved lobes with cerata in total (placed partly in a scallop-like pattern, if counting only the ceratal lobe-based groups, there will be correspondingly fewer in number) and separately placed cerata along dorsal edges, which are formed by a reduced discontinuous notal edge. Apices of cerata gradually pointed, with elongated cnidosacs. Digestive gland diverticulum fills significant volume of the cerata. Anal opening pleuroproctic on right side below middle ceratal lobes. Reproductive openings lateral, below first-second and third-fifth ceratal lobes/separate cerata.

Colour ( Fig. 7A–D, L, S) Background colour semi-transparent whitish to greyish. Cerata opaque yellowish to lemon-coloured (granulated when magnified) throughout most of the length with somewhat lighter bases. Cnidosacs in subapical parts of cerata darker yellowish-orange. Apical parts of cerata without opaque cap of white pigment, semi-transparent. Rhinophores covered with yellowish-whitish pigment over almost their entire length. The blackish ampulla, seminal receptacles, vas deferens and other ducts, as well as the lighter greyish (with darker elements inside) thick prostate, shine through the anterior part of the dorsal side and are characteristically well visible in living specimens ( Fig. 7A, D, L, S). Whitish gonad shines through the mid and posterior parts.

Jaws ( Fig. 7G–I, P) Jaws oval-triangular. Edge of masticatory processes bears up to about 30 denticles that may form compound row of thickened denticles comprised of some smaller tubercles.

Radula ( Fig. 7E, F, M, N, O) Radula formula in two specimens 17–18 × 0.1.0. Central teeth considerably narrow, elongate-triangular, rather feather-shaped with short, narrow, commonly double cusps. Central teeth bear up to at least 11 well-defined distinct, but denticles narrowly-arranged toward cusp. Lateral teeth absent.

Reproductive system ( Fig. 7J, K, Q, R, T, U) Hermaphroditic duct leads to oval swollen ampulla. Vas deferens moderately long, narrow, somewhat convoluted, leads to very distinct, thick prostate. Penial sheath is oval. Penis is broadened conical, bears long, distinctly curved stylet with large oblique opening. Oviduct connects through insemination duct into female gland complex. Proximal receptaculum seminis elongate, moderately swollen. Distal receptaculum seminis present, rounded, almost sessile on a short stalk.

Ecology: Shallow waters, stony habitats.

Distribution: So far reliably known only from the Pacific side of middle Japan (Honshu). Potentially may occur in other parts of Honshu and more southern main Japanese Islands.

Remarks: Hantazuia yugoikedai sp. nov. is externally similar to Hantazuia kimotoi sp. nov., but reliably differs from it by the shape of its copulative stylet, which is significantly longer and more curved ( Fig. 7J, K, Q, T). The potential external difference between H. yugoikedai sp. nov. and H. kimotoi sp. nov. is that the latter has potentially longer anterior foot corners and possibly is somewhat smaller in length at the adult stage ( Fig. 7B, D), but this needs to be checked further. Uncorrected COI p -distances within the Hantazuia yugoikedai sp. nov. clade are 0.3%–0.5%. The COI uncorrected p -distances between the H. yugoikedai sp. nov. clade and the H. kimotoi sp. nov. clade are 12.3%–12.8%, between the H. yugoikedai sp. nov. clade and the H. imagawai sp. nov. clade are 12.3%–12.8%.