Gymnodoris fassioae De Souza-Canal & Valdés sp. nov.

urn:lsid:zoobank.org:act: 558047D3-D711-417F-A173-FD05C8111161

(Fig. 17H–I, 18D, 19C–E)

Type material. Holotype: New Caledonia: North Province: Koumac, Passe Deverd (20°44.6'S, 164°15.7'E), 21 m depth [Koumac 2.1 Expedition, stn. KR623], 21 Sep 2018, 1 specimen 5 mm preserved length (MNHN-IM-2019- 26502, isolate JD24).

Description. Body oval to elongate, with numerous, small conical to elongate tubercles of varying sizes. Notal rim distinct, with several larger tubercles than those on dorsum, velum absent, notal rim fuses into head forming a protuberance, edged by arch or small tubercles anterior to rhinophores (Fig. 18D). Color translucent white, tubercles red with blurry edges; longitudinal lines of blurry red pigment joining some tubercles; posterior end of foot translucent grey with red tip. Internal organs visible through body wall as orange, white masses. Rhinophores very close together, bulbous, with 8 lamellae, stalk white, club red. Gill with 35 small, elongate, simple, translucent leaves with red tips, opaque white bases, arranged in circle around anus, opened posteriorly. Foot narrower than notum, opaque white. Oral tentacles small, blunt.

Radular formula 24 × 21.0. 21 in the 5 mm preserved length holotype (MNHN-IM-2019-26502). Innermost lateral teeth small, broad, irregular bases, with central curved cusp (Fig. 19C). Other lateral teeth elongate, with broad bases, long, slightly curved cusps (Fig. 19E).

Reproductive system with a large, broad, slightly curved ampulla, connecting to female gland complex, prostate (Fig. 17H). Prostate tubular, curved around bursa copulatrix, narrowing into a highly convoluted deferent duct, opening into a common atrium with vagina. Vagina long, narrow, slightly curved, connecting into bursa copulatrix near seminal receptacle connection. Bursa copulatrix ovoid, about five times as large as spherical seminal receptacle. Penial spines slightly curved, elongate (about 80 µm long), with narrow bases (Fig. 17I).

Phylogenetic position. Gymnodoris fassioae sp. nov. is sister to Gymnodoris sp. 18 (PP: 1, MLB: 99) but the position of these two species within the overall phylogeny of Gymnodoris remains unresolved (Fig. 1A).

Etymology. This species is named in honor of Dr. Giulia Fassio in appreciation for her help and support during the expeditions to New Caledonia.

Remarks. Gymnodoris fassioae sp. nov. is externally similar in body shape to Gymnodoris inariensis Hamatani & Osumi, 2003 described from Kagoshima Bay, Japan. Both species have rhinophores very close to each other at the base, a well-defined notal rim, and an anterior protuberance instead of a velum. However, there are clear differences between the two species, for instance, G. inariensis lacks a gill, which is present in G. fassioae sp. nov., and G. inariensis is blackish with densely scattered, minute dark brown-black spots, whereas G. fassioae sp. nov. is translucent white, with red tubercles with blurry edges. No other species included in Knutson & Gosliner (2022) is similar externally or genetically to G. fassioae sp. nov.