Gymnodoris citrina ( Bergh, 1877 )

Gymnodoris citrina ( Bergh, 1877) View in CoL

( Fig. 3 View FIGURE 3 )

Trevelyana citrina Bergh, 1877: 442–443 View in CoL , pl. 41, fig. 5, pl. 56, figs. 18–25. Type locality: “Ins. Pelew” [= Palau].

? Trevelyana perlucens Risbec, 1928: 185–189 , text figs. 57, 57bis, pl. 1, fig. 12, pl. 5, fig. 1. Type locality: Several localities including Rocher à la Voile, Nouméa, New Caledonia, Canala , New Caledonia , Paagoumène , New Caledonia , and Île N’ du Kué [= Île Ndukué], Baie Saint Vincent, New Caledonia .

Material examined. New Caledonia: North Province: Koumac ( 20°37.4'S, 164°09'E), 3 m depth [ Koumac 2.3 Expedition , stn. KB624], 5 Nov 2019, 1 specimen 4 mm preserved length (MNHN-IM-2019-26418, isolate JD71) GoogleMaps . New Caledonia: North Province: Poum, South Yandé Is. ( 20°4.57'S, 163°49.59'E), 0 m depth [ABC Poum Expedition, stn. ABC58 ], 20 Jun 2023, 1 specimen 7 mm preserved length (MNHN-IM-2019-26419, isolate JD104); 1 specimen 6 mm preserved length (MNHN-IM-2019-26420, isolate JD123) GoogleMaps . New Caledonia: South Province: Nouméa, Rocher à la Voile ( 22°18.2'S, 166°26'E), 1 m depth, 11 Nov 2021, 1 specimen 9 mm preserved length [rocky coastal area] (MNHN-IM-2019-26439, isolate JD148), leg. Y. Thévenet GoogleMaps ; 2 m depth, 3 Jan 2022, 1 specimen 4 mm preserved length [rocky coastal area] (MNHN-IM-2019-26437, isolate JD147), leg. A. Doulas; 1 m depth, 17 Aug 2022, 1 specimen 6 mm preserved length [rocky coastal area] (MNHN-IM-2019-26440, isolate JD150), leg. A. Doulas. New Caledonia: South Province: Nouméa, Pointe Artillerie ( 22°17'S, 166°25.9'E), 1–2 m depth, 2023, 6 Sep 2023, 1 specimen 2 mm preserved length [rocky coastal area] (MNHN-IM-2019-26477, isolate JD183), leg. A. Doulas GoogleMaps ; 1 specimen 11 mm preserved length, coastal rocky zone (MNHN-IM-2019-26522, not sequenced), leg. A. Doulas. New Caledonia: Loyalty Is.: Ouvéa, Plage de Teuta ( 20°24.133'S, 166°36.68'E), 0 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUM34 ], 14 Jan 2024, 1 specimen 5 mm preserved length (MNHN-IM-2019-26438, isolate JD166) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, Tiberia ( 20°28.5'S, 166°35.66'E), 0 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUM35 ], 14 Jan 2024, 1 specimen 11 mm preserved length (MNHN-IM-2019-26507, JD181) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, Pont de Mouly ( 20°41.91'S, 166°28.33'E), 5 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUP37, night dive], 14 Jan 2024, 1 specimen 7 mm preserved length (MNHN-IM-2019-26441, isolate JD177) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, Tiberia ( 20°41.15'S, 166°38.55'E), 0 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUM42 ], 15 Jan 2024, 1 specimen 13 mm preserved length (MNHN-IM-2019-26442, isolate JD170) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, West of Ilôt Unyee ( 20°24.3'S, 166°31.3'E), 0 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUM49 ], 16 Jan 2024, 1 specimen 12 mm preserved length (MNHN-IM-2019-26443, isolate JD162) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, West end of Pointe Nord ( 20°24.58'S, 166°31.25'E) [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUP51 ], 16 Jan 2024, 1 specimen 12 mm preserved length (MNHN-IM-2019-26444, isolate JD156); 1 specimen 4 mm preserved length (MNHN-IM-2019-26447, isolate JD175) GoogleMaps . New Caledonia: Loyalty Is.: Ouvéa, Hoony ( 20°26.45'S, 166°38.45'E), 0 m depth [ Quinzaine des Nudibranches Ouvéa Expedition , stn. QUM64 ], 19 Jan 2024, 1 specimen 8 mm preserved length (MNHN-IM-2019-26445, isolate JD155); 1 specimen 10 mm preserved length (MNHN-IM-2019-26446, isolate JD167) GoogleMaps .

Description. Body oval to elongated, narrow, with numerous small, low, conical tubercles ( Fig. 3 View FIGURE 3 ). Velum well developed, with 10–14 conical, elongate papillae; notal rim absent, velum merges into notum behind rhinophores. Posterior end of foot narrowing into long, pointy “tail.” Color translucent dirty-white, with internal organs visible as orange, white blotches; tubercles, velum papillae orange-red, very inconspicuous in some specimens; posterior end of foot translucent grey. Rhinophores bulbous, with elongate, narrow tip; 12–20 lamellae, uniformly cream or brown club, translucent white stalk. Gill with 9–12 large, broad, bipinnate leaves, forming complete circle around the anus. Gill leaves uniformly white to yellow. Foot wider than notum, surrounded by white to orange line of variable within some specimens. Anterior end of foot with well-developed, blunt oral tentacles.

Phylogenetic position. Gymnodoris citrina is a member of a large clade (PP: 1, MLB: 81) including Gymnodoris alba ( Bergh, 1877) , Gymnodoris brunnea Knutson & Gosliner, 2014 , Gymnodoris pseudobrunnea Knutson & Gosliner, 2014 , and several undescribed species: Gymnodoris sp. 9 , Gymnodoris sp. 12, Gymnodoris sp. 14, Gymnodoris sp. 15, Gymnodoris sp. 16, Gymnodoris sp. 53, Gymnodoris sp. 56, Gymnodoris sp. A , and Gymnodoris sp. ( Fig. 1A View FIGURE 1 ). However, the position of Gymnodoris citrina within this clade and the position of the clade within the larger phylogeny of Gymnodoris are unresolved ( Fig. 1A View FIGURE 1 ).

Remarks. Trevelyana citrina was originally described by Bergh (1877) from Palau, with the characteristics of the live animal extracted from a color plate by Semper (reproduced by Bergh, 1877, pl. 41, fig. 5) as follows: “color was light egg yellow, with scattered ocher-yellow dots on the dorsum and sides, which also appeared on the gill leaves.” The identity of this species has been interpreted by several authors to correspond to a species variable in color (white, yellow or red), characterized by having a distinct velum with 8–10 conical projections, minute, conical reddish-orange tubercles, a well-developed gill with numerous tripinnate leaves oriented inward, and large, flattened, triangular anterior ends of the foot with large oral tentacles (see Rudman & Darvell, 1990; Yonow, 2008; Gosliner et al., 2018; Kil et al., 2020), which also corresponds to the material here reported from New Caledonia. The identity of the New Caledonia specimens is further corroborated by sequence data, which is conspecific (in the species delimitation analyses) with the specimens studied by Knutson & Gosliner (2022) identified as G. citrina .

Risbec (1928) described Trevelyana perlucens from New Caledonia based on numerous specimens from various localities, as a yellowish-white species with yellow or red dots distributed irregularly on small papillae, a strongly projecting frontal veil with around ten papillae, and well-developed swellings on the anterior end of the foot with two conspicuous tentacles. These characteristics closely match those of the material here examined, and therefore we propose that T. perlucens could be a synonym of G. citrina as currently understood by Knutson & Gosliner (2022). This synonymy has already been suggested by Risbec (1928) himself by noting that T. perlucens could be the same species as Trevelyana bicolor Alder & Hancock, 1864 , which he also considered synonymous with G. citrina (as Trevelyana ), a suggestion later endorsed by Macnae (1957). However, more recently other authors indicated that G. bicolor and G. citrina are distinct ( Yogesh Kumar et al., 2021).

Based on the number of specimens here examined and the records by Risbec (1928), G. citrina appears to be common in New Caledonia and distributed over the entire country. However, the specimens from Poindimié identified as G. citrina by Hervé (2010) probably correspond to other species and are discussed below.