Gymnodoris sp. 9

(Figs. 11A–K)

Material examined. New Caledonia: North Province: Koumac, Ilôt Rat (20°33.4'S, 164°10.9'E), 0 m depth [Koumac 2.1 Expedition, stn. KM200, sand-mud flat with seagrass; reef flat, rocky shore with living/dead corals], 4 Sep 2018, 1 specimen 8 mm preserved length (MNHN-IM-2019-26394, isolate JD59). New Caledonia: North Province: Koumac, Infernet Reef (20°37.1'S, 164°15'E), 3 m depth [Koumac 2.1 Expedition, stn. KR302, at the foot of the reef, sandy sediment with silt, coral debris, and seagrass], 7 Sep 2018, 1 specimen 5 mm preserved length (MNHN-IM-2019-26435, isolate JD70). New Caledonia: North Province: Koumac, Ilôt Kendec (20°40.1'S, 164°15.4'E), 0 m depth [Koumac 2.1 Expedition, stn. KM302, living corals, coral rubble, sand patches], 9 Sep 2018, 1 specimen 10 mm preserved length (MNHN-IM-2019-26395, isolate JD07). New Caledonia: South Province: Nouméa, Ilôt Song, Ouémo (22°16.91'S, 166°28.84'E), 1–6 m depth [Quinzaine des Nudibranches Expedition, stn. QNPF-DA, detrital sandy-muddy, live Porites], 6 Sep 2022, 1 specimen 9 mm preserved length (MNHN-IM-2019-26396, isolate JD85). New Caledonia: South Province: Ouémo, Platier Ricaudy (22°18.67'S, 166°27.49'E), 0.5 m depth [Quinzaine des Nudibranches Expedition, stn. QNAV-FA], 4 Sep 2022, 1 specimen 6 mm preserved length (MNHN-IM-2019-26436, isolate JD131). New Caledonia: North Province: Poum, Mouac Is. (20°12.84'S, 164°0.61'E), 0 m depth [ABC Poum Expedition, stn. ABC46], 18 Jun 2023, 1 specimen 7 mm preserved length (MNHN-IM-2019-26434, isolate JD140). New Caledonia: North Province: Poum, Bay of the Grotte (20°2'S, 163°47.92'E), 0 m depth [ABC Poum Expedition, stn. ABC52], 19 Jun 2023, 1 specimen 7 mm preserved length (MNHN-IM-2019-26431, isolate JD122); 1 specimen 7 mm preserved length (MNHN-IM-2019-26432, isolate JD141). New Caledonia: North Province: Poum, Mouac Is. (20°13.02'S, 164°1.4'E), 0 m depth [ABC Poum Expedition, stn. ABC63], 21 Jun 2023, 1 specimen 9 mm preserved length (MNHN-IM-2019-26433, isolate JD99). New Caledonia: Loyalty Is.: Ouvéa, Pont de Mouly (20°41.91'S, 166°28.33'E) [Quinzaine des Nudibranches Ouvéa Expedition, stn. QUP63, night dive], 18 Jan 2024, 1 specimen 9 mm preserved length (MNHN-IM-2019-26516, isolate JD153). New Caledonia: South Province: Nouméa, Ilôt Song (22°16.91'S, 166°28.84'E), 10 m depth, 28 Jun 2022, 1 specimen 11 mm preserved length (MNHN-IM-2019-26518, isolate JD144), leg. Y. Thévenet.

Description. Body narrow, elongate, with numerous low, conical tubercles of varying sizes (Figs. 11A–K). Anterior end of notum with distinct velum having 15–18 small papillae; notal rim absent, velum merges with notum behind rhinophores. Posterior end of foot broad, tapering into pointy “tail.” Color translucent white, tubercles, velum papillae yellow-orange; posterior end translucent grey. Internal organs, posterior branched glandular structure visible through body wall. Rhinophores bulbous with narrow tips, 12–14 lamellae, cream, brow, or reddish, with apical orange-red dot. Gill with 8 short, irregular, bipinnate leaves, translucent white, sometimes with small orange dots, opaque white bases, arranged in circle around anus, opened posteriorly. Foot wider than notum, translucent yellow. Oral tentacles large, flap-like.

Phylogenetic position. Gymnodoris sp. 9 is the most basal member of a well-supported clade (PP: 1, MLB: 100) also including Gymnodoris alba and Gymnodoris sp. 49, which are sister to one another (PP: 1, MLB: 100) (Fig. 1A).

Remarks. This undescribed species is similar to G. citrina, both having the anterior margin of the head with a distinctive row of low tubercles, but the anterior end of the foot has two flap-like oral tentacles, instead of a well-developed but blunt oral tentacles in G. citrina . Moreover, G. citrina lacks a glandular structure behind the gill.

Gymnodoris sp. 9 appears to be widespread in the Indo-Pacific region (Gosliner et al., 2018). Knutson & Gosliner (2022) studied specimens from Papua New Guinea, Vanuatu, and Saudi Arabia. Also, possibly reported from French Polynesia (Boutet et al., 2020) as Gymnodoris sp. 2, from Okinawa, Japan by Nakano (2018) as Gymnodoris sp. 17 and G. citrina (large photo), and from Hong Kong, China by Rudman & Darvell (1990: pl. 4, fig. C) as G. citrina atypical form. Very common in New Caledonia, it has possibly been reported from Nouméa by Hervé (2010) as Gymnodoris sp. 2 (small photo).