Gymnodoris nigricolor Baba, 1960

Souza-Canal, Jade De, Ángel, Rie Nakano & Valdés, Ángel, 2025, Gymnodoris nigricolor Baba, 1960 (Mollusca, Nudibranchia, Polyceridae) is a species complex, Zoosystema 47 (17), pp. 315-326 : 320

Gymnodoris nigricolor Baba, 1960

( Figs 2A, B ; 3A, B ; 4A, B )

Gymnodoris nigricolor Baba, 1960: 72 , pl. 5, figs 1A, B.

MATERIAL EXAMINED.— New Caledonia • 1 specimen 5 mm preserved length, dissected; Koumac , East of Karembé; 20°39.6’S, 164°17.5’E; 2-5 m; 27.IX.2018; Koumac 2.1 Stn KR 636; isolate JD67; MNHN-IM-2019-26208 • 1 specimen 6 mm preserved length, dissected; Koumac , Channel between Tangadiou Islet and Magone; 20°33.9’S, 164°13.2’E; 7-8 m; 20.IX.2018; Koumac 2.1 Stn KR 224; isolate JD27; MNHN-IM-2019-26209 .

DESCRIPTION

Body elongate, smooth, lacking tubercles ( Fig. 2A, B ). 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 short, conical, fused together at base. Rhinophoral club occupying entire visible length, with six transverse lamellae. Gill composed of 10-11 simple leaves, arranged in a circle.

Radular formula 10 × 7.1.1.0.1.1. 7 in a 6 mm-long specimen (MNHN-IM-2019-26209, isolate JD27) and 9 × 6.1.1.0.1.1. 6 in a 5 mm-long specimen (MNHN-IM-2019-26208, isolate JD67). Rachidian teeth absent ( Fig. 3A ). Innermost lateral teeth hook-shaped, with elongate cusp, 3-4 denticles ( Fig. 3A ). Second innermost lateral teeth broad, with wide base, two lateral flattened extensions, large, irregular, elongate central cusp ( Fig. 3A ). Outermost teeth similar in size, elongated, hamate with wide base, long conical cusp ( Fig. 3B ). Labial cuticle smooth.

Reproductive system ( Fig. 4A ) with pyriform ampulla connecting with both female gland complex, prostate. Prostate tubular, convoluted, with several folds, much wider than ampulla. Prostate narrowing into curved duct before expanding into elongate, convoluted deferent duct, narrower than prostate. Vagina as wide as deferent duct, mostly straight, curving before connecting directly into bursa copulatrix. Seminal receptacle small, pyriform, connecting to oval bursa copulatrix opposite to vaginal connection; uterine duct short, connected to female gland complex. Bursa copulatrix twice as large as seminal receptacle. Penis with 200-400 mm-long, elongate spines with narrow bases ( Fig. 4B ).

BIOLOGY

Original described from Japan ( Baba 1960). This species was reported from New Caledonia by Hervé (2010), based on a photograph of a specimen found in Nouméa, but the identity of the specimen is unclear. The present is the first confirmed record of this species from New Caledonia where it is rare, found on sand at 7-8 m depth. The specimens were collected by direct collection while scuba diving. The feeding behavior was not observed, but specimens identified as G. nigricolor from Japan were reported to feed on the soft tissue of gobby fish fins ( Osumi & Yamasu 1994, 2000).

REMARKS

Baba (1960) described G. nigricolor based on a single specimen collected on a muddy bottom at 2 m depth in Misaki, Sagami Bay, Japan, as being “very distinct in coloring and in the shape of the radula teeth. Length 4 mm. Body smooth. Gills small, consisting of 9 plumes arranged in a semicircle open behind. Back and sole uniformly bluish black; rhinophores and gills also bluish black. Radula formula 22 × 7-8.1.0.1.7-8. First lateral broad and tricuspidate (the median cusp sharp, the lateral cusps blunt). Next laterals pyriform.”

Two specimens examined here from New Caledonia presents the same morphological features as described by Baba (1960: fig. 1A, B) for G. nigricolor , with a high resemblance in the radular morphology, having a truncated triangular inner most teeth with a large central conical cusp and two lateral flat cusps, and elongated hamate outermost lateral teeth. Baba’s (1960) illustration of the live animal also shows the rhinophores are fused at the base. Based on these similarities we are confident the two specimens here examined belong to this species. Unfortunately, there are no other anatomical descriptions of specimens assigned to G. nigricolor from other localities that could be used to compare with the material here examined.

Figures

FIG. 2.— Photographs of live animals of the Gymnodoris nigricolor species complex: A, B, Gymnodoris nigricolor Baba, 1960, specimen MNHN-IM-2019-26208, isolate JD67 (A), specimen MNHN-IM-2019-26209, isolate JD27 (B); C-J, Gymnodoris boussionae n. sp. specimen MNHN-IM-2019-26204, isolate JD23 (C), specimen MNHN-IM-2019-26203, isolate JD35 (D), specimen MNHN-IM-2019-26206, isolate JD41 (E), specimen MNHN-IM-2019-26200, isolate JD43 (F), specimen MNHN-IM-2019-26205, isolate JD39 (G), specimen MNHN-IM-2019-26299, isolate JD51 (H), specimen MNHN-IM-2019-26207, isolate JD44 (I), specimen MNHN-IM-2019-26201, isolate JD10 (J); K, Gymnodoris nagoensis n. sp., specimen from Sunabe,Okinawa Prefecture,Japan,NSMT-Mo 79541,photo H.Tokura.

FIG. 3.— SEM of the radula of the Gymnodoris nigricolor species complex: A, B, Gymnodoris nigricolor Baba, 1960, specimen MNHN-IM-2019-26209, isolate JD27, innermost teeth (A) and outer lateral teeth (B); C-D, Gymnodoris boussionae n. sp., specimen MNHN-IM-2019-26203, isolate JD35, innermost teeth (C) and outer lateral teeth (D); E-F, Gymnodoris nagoensis n. sp., specimen from Sunabe, Okinawa Prefecture, Japan, NSMT-Mo 79541, innermost teeth (E) and outer lateral teeth (F). Scale bars: A, 30 μm; B, D, 20 μm; C, 30 μm; E, F, 10 μm.

FIG. 4.— Drawings of the reproductive system of the Gymnodoris nigricolor species complex: A, B, Gymnodoris nigricolor Baba, 1960, specimen MNHN- IM-2019-26209, isolate JD27, reproductive system (A) and penial spines (B); C, D, Gymnodoris boussionae n. sp., specimen MNHN-IM-2019-26203, isolate JD35, reproductive system (C) and penial spines (D); E, F, Gymnodoris nagoensis n. sp. specimen from Sunabe, Okinawa Prefecture, Japan, NSMT-Mo 79541, reproductive system (E) and penial spines (F). Scale bars: A, C, E, 1 mm; B, D, F, 100 μm. Abbreviations: see Material and methods.