Gymnodoris nagoensis Souza-Canal, Ángel & Valdés, 2025, n. sp.

Gymnodoris nagoensis n. sp. (Figs 2K; 3E, F; 4E, F) urn:lsid:zoobank.org:act: 4EAC8527-DA41-4C9A-A3DD-AB36DFDCA528 TYPE MATERIAL. — Holotype. Japan • specimen 6 mm preserved length, dissected; Okinawa Prefecture; Nago; Kouki; 26°32.8’N, 127°57.7’E; 31.V.2012; 10 m; isolate JP01; NSMT-Mo 79540. OTHER MATERIAL EXAMINED.— Japan • 2 specimens 4 mm preserved length, dissected; Okinawa Prefecture, Ginowan, Sunabe; 26°19.4’N, 127°44.6’E; 23.II.2010; 16 m; NSMT-Mo 79541 • 1 specimen 4 mm preserved length, dissected; Kagoshima Prefecture; Amami Ōshima Island; Tebiro Beach; 28°24.1’N, 129°37.2’E; 9.III.2010; 9 m; NSMT-Mo 79542. ETYMOLOGY. — Named after Nago, Okinawa Prefecture, Japan, the type locality of this species. DESCRIPTION Body elongate, smooth, lacking tubercles (Fig. 2K). Body color velvet black, with blurry neon-blue lines visible on mantle margin under certain light conditions. Rhinophores and branchial leaves with same color as dorsum. Rhinophores elongate, conical, not fused together at base.Rhinophoral club occupying entire visible length, with transverse five lamellae. Gill composed of 10 simple gill leaves, lacking lamellae, arranged in a circle. Radular formulae 18 × 11.1.0.1. 11 in a 4 mm-long specimen (NSMT-Mo 79541) and 18 × 12.1.0.1. 12 in a 6 mm-long specimen (NSMT-Mo 79540). Rachidian teeth absent. Innermost lateral teeth hamate, with very elongate, curved cusp, no denticles (Fig. 3E). Outer later teeth much smaller than innermost teeth, further decreasing in size gradually towards outer edge, hamate with wide base, long curved cusp (Fig. 3F). Labial cuticle smooth. Reproductive system (Fig. 4E) with simple, pyriform ampulla connecting to both female gland, prostate. Prostate tubular, curved, much narrower than female gland. Prostate narrowing into relatively convoluted duct before expanding into short deferent duct. Deferent duct narrower than ampulla at its widest point. Vagina slightly curved, as wide as deferent duct, connecting directly into bursa copulatrix. Seminal receptacle small, oval, connecting to large, nearly spherical bursa copulatrix, in expanded region near vaginal connection; uterine duct short, connecting to female gland complex. Bursa copulatrix several times as large as seminal receptacle. Penis with 200- 300 mm-long, elongate spines with narrow bases, elongate cusps (Fig. 4F). BIOLOGY Found on sandy/silty bottoms at depths of 3-30 meters on Okinawa and Amami Ōshima island. When individuals of G. nagoensis n. sp. find a goby hole, they crawl into it. It seems that the nudibranch feeds on the fins of the goby; sometimes several individuals feed on the fins of a goby at the same time. REMARKS Gymnodoris nagoensis n. sp. is genetically very similar to G. nigricolor Baba, 1960 (Supplementary material 2; Fig.1B) and recovered as the same species in the ASAP analysis but distinct in the bPTP analysis. Unfortunately, we were only able to amplify COI from one specimen despite multiple attempts. However, G. nagoensis n. sp. is anatomically different from all other species here examined. Externally, the rhinophores of G. nagoensis n. sp. are proportionally longer and have a reduced number of branchial leaves. The radular morphology of G. nagoensis n. sp. is similar to that of G. boussionae n. sp. but clearly distinct from that of G. nigricolor. The innermost teeth of G. nagoensis n. sp. are very elongate in comparison to mid-lateral teeth and lack denticles, whereas the innermost teeth of G. nigricolor are approximately the same size as the mid-lateral teeth, with truncated triangles, a large central conical cusp, and two lateral flat cusps. The teeth of G. nagoensis n. sp. are very similar to those of G. boussionae n. sp. even though these two species are phylogenetically more distant, and their reproductive anatomy is substantially different. The reproductive anatomy of G. nagoensis n. sp. is unique, having large, elongate penial spines with small bases, a bursa copulatrix several times larger than the seminal receptacle and a very short deferent duct. This combination of traits is not present in G. boussionae n. sp. or G. nigricolor and clearly differentiates G. nagoensis n. sp. from the other two species.