Gymnodoris plebeia ( Bergh, 1877 )

Souza-Canal, Jade De & Valdés, Ángel, 2025, The genus Gymnodoris Stimpson, 1855 (Mollusca, Nudibranchia) in New Caledonia, with descriptions of eleven new species, Zootaxa 5710 (1), pp. 1-73 : 29-30

Gymnodoris plebeia ( Bergh, 1877)

( Fig. 4 )

Trevelyana plebeia Bergh, 1877: 446–449 , pl. 54, figs. 26–35. Type locality: Aibukit, Palau.

Gymnodoris sp. 2 — Gosliner et al., 2018: 71.

Gymnodoris sp. R— Knutson & Gosliner, 2022.

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 and dead corals], 3 Sep 2018, 1 specimen 11 mm preserved length (MNHN-IM-2019-26366, isolate JD03) . New Caledonia: North Province: Koumac, Back Reef (white bottoms) ( 20°38.3'S, 164°12.4'E), 7–15 m depth [Koumac 2.1 Expedition, stn. KM607 ], 5 Sep 2018, 1 specimen 20 mm preserved length (MNHN-IM-2019-26368, isolate JD06) . New Caledonia: North Province: Koumac, NW Infernet (exterior) ( 20°35.5'S, 164°12.9'E), 10 m depth [Koumac 2.1 Expedition, stn. KR619, sandy-muddy, algal patches], 19 Sep 2018, 1 specimen 16 mm preserved length (MNHN-IM-2019-26367, isolate JD05) . New Caledonia: North Province: Koumac, Pointe Pandop ( 20°34.9'S, 164°16.6'E), 0 m depth [Koumac 2.2 Expedition, stn. KM100 , rocky shore, rubble, sand, mud, seagrasses], 28 Feb 2019, 1 specimen 19 mm preserved length (MNHN-IM-2019-26371, isolate JD55) . New Caledonia: North Province: Koumac ( 20°38.4'S, 164°16.5'E) [Koumac 2.2 Expedition, stn. KR252], 28 Feb 2019, 1 specimen 11 mm preserved length (MNHN-IM-2019-26369, isolate JD33); 1 specimen 13 mm preserved length (MNHN-IM-2019- 26374, isolate JD40); 1 Mar 2019, 1 specimen 16 mm preserved length (MNHN-IM-2019-26365, isolate JD04) . New Caledonia: North Province: Koumac ( 20°35.6'S, 164°16.3'E) [Koumac 2.2 Expedition, stn. KR230], 2 Mar 2019, 1 specimen 2 mm preserved length (MNHN-IM-2019-26514, not sequenced); 1 specimen 2 mm preserved length (MNHN-IM-2019-26515, not sequenced) . New Caledonia: North Province: Koumac ( 20°33.1'S, 164°13.9'E), 6 m depth [Koumac 2.3 Expedition, stn. KR902], 1 Nov 2019, 1 specimen 9 mm preserved length (MNHN-IM-2019-26373, isolate JD96) . New Caledonia: North Province: Koumac ( 20°38.9'S, 164°18'E), 7 m depth [Koumac 2.3 Expedition, stn. KR914], 15 Nov 2019, 1 specimen 9 mm preserved length (MNHN-IM-2019-26370, isolate JD32) . New Caledonia: North Province: Koumac ( 20°35.4'S, 164°16.8'E), 7 m depth [Koumac 2.3 Expedition, stn. KD584 ], 21 Nov 2019, 1 specimen 12 mm preserved length (MNHN-IM-2019-26372, isolate JD30) . New Caledonia: North Province: Poum, Phaayo ( 20°9.68'S, 164°1.28'E) [ABC Poum Expedition, stn. ABC18, island slopes], 6 Jun 2023, 1 specimen 18 mm preserved length (MNHN-IM-2019-26402, isolate JD118); 1 specimen 13 mm preserved length (MNHN-IM-2019-26403, isolate JD121) . New Caledonia: North Province: Poum, Ilôt Bayu ( 20°7.53'S, 164°4.71'E), 0 m depth [ABC Poum Expedition, stn. ABC58 ], 13 Jun 2023, 1 specimen 12 mm preserved length (MNHN-IM-2019-26401, isolate JD102) . New Caledonia: North Province: Poum, Tribu Juu ( 20°8.59'S, 164°1'E) [ABC Poum Expedition, stn. ABC26 ], 14 Jun 2023, 1 specimen 15 mm preserved length (MNHN-IM-2019-26404, isolate JD120) . New Caledonia: North Province: Poum, Récif Pwiac ( 20°1.64'S, 164°5.86'E) [ABC Poum Expedition, stn. ABC27, deep flats], 14 Jun 2023, 1 specimen 14 mm preserved length (MNHN-IM-2019- 26408, isolate JD129) . New Caledonia: North Province: Poum, Ilôt Bayu ( 20°7.56'S, 164°4.72'E) [ABC Poum Expedition, stn. ABC78, island slopes], 22 Jun 2023, 1 specimen 14 mm preserved length (MNHN-IM-2019-26406, isolate JD133); 1 specimen 14 mm preserved length (MNHN-IM-2019-26409, isolate JD128); 1 specimen 16 mm preserved length (MNHN-IM-2019-26410, isolate JD137) . New Caledonia: North Province: Poum, Arama ( 20°14.63'S, 164°12.15'E) [ABC Poum Expedition, stn. ABC80 ], 23 Jun 2023, 1 specimen 16 mm preserved length (MNHN-IM-2019-26407, isolate JD130) . New Caledonia: North Province: Poum, Ilôt St. Phalles ( 20°6.74'S, 164°6.47'E) [ABC Poum Expedition, stn. ABC88 ], 24 Jun 2023, 1 specimen 16 mm preserved length (MNHN-IM-2019-26408, isolate JD119) .

Description. Body oval to elongated, with numerous, densely arranged, large, rounded tubercles ( Fig. 4 ). Velum distinct, with several tubercles; notal rim absent, velum merges with notum behind rhinophores. Posterior end of foot tapering slightly into broad “tail.” Body color dark grey to brown, tubercles yellowish white to cream, sometimes with yellow pigment in center. Rhinophores elongate, with 10–12 lamellae, club white antero-distally (sometimes with yellow tips), brown proximally, stalk pale brown. Gill with 5–6 large, broad, tripinnate leaves, opaque dark brown, main rachises white to cream externally. Foot wider than notum, surrounded by pale cream or white broad line. Oral tentacles short, blunt, white.

Phylogenetic position. The phylogenetic position of Gymnodoris plebeia is unresolved ( Fig. 1A ) but the monophyly of this species is well supported (PP: 1, MLB: 100) ( Fig. 1A ).

Remarks. Bergh (1877) originally described Trevelyana plebeia from Palau as a mostly light olive-brown-gray species with numerous whitish knots. This is a very characteristic color pattern only found in one Western Pacific species of Gymnodoris , illustrated by Hervé (2010) as G. plebeia and by Gosliner et al. (2018) as G. sp. 2. Moreover, specimens sequenced by Knutson & Gosliner (2022) and named Gymnodoris sp. R are genetically conspecific with the material here assigned to G. plebeia , based on species delimitation analysis results.

Gymnodoris plebeia is locally very common in New Caledonia and as mentioned above has been recorded in Ilôt Maître by Hervé (2010) and from an undermined locality by Gosliner et al. (2018), who also reported it from Australia.

Figures

FIGURE 1. A. Bayesian consensus phylogenetic tree of the concatenated dataset including PP above branches and MLB below branches. Branches fully supported (PP: 1, MLB: 100) marked with asterisks. New species described in this paper highlighted in red font and illustrated; other species reported from New Caledonia in this study highlighted in blue font. Clades are collapsed according to the results of the ASAP and bPTP species delimitation analyses. B. Histogram representing the distance plot from the ASAP analysis using the COI gene showing pairwise p-distances (Kimura 2 model) among candidate species. The dashed line represents the distance threshold provided by the lowest ASAP score for species delimitation.

FIGURE 4. Gymnodoris plebeia (Bergh, 1877), photographs of live animals showing color variation. A. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26366, isolate JD03). B. Specimen from Koumac, New Caledonia (MNHN-IM- 2019-26368, isolate JD06). C. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26367, isolate JD05). D. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26369, isolate JD33). E. Specimen from Koumac, New Caledonia (MNHN- IM-2019-26365, isolate JD04). F. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26514, not sequenced). G. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26370, isolate JD32). H. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26374, isolate JD40). I. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26371, isolate JD55). J. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26373, isolate JD96). K. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26372, isolate JD30). L. Specimen from Poum, New Caledonia (MNHN-IM-2019-26401, isolate JD102). M. Specimen from Koumac, New Caledonia (MNHN-IM-2019-26515, not sequenced). N. Specimen from Poum, New Caledonia (MNHN-IM-2019-26403, isolate JD121). O. Specimen from Poum, New Caledonia (MNHN-IM-2019-26402, isolate JD118). P. Specimen from Poum, New Caledonia (MNHN-IM-2019-26409, isolate JD128). Q. Specimen from Poum, New Caledonia (MNHN-IM-2019-26404, isolate JD120). R. Specimen from Poum, New Caledonia (MNHN-IM-2019-26408, isolate JD129). S. Specimen from Poum, New Caledonia (MNHN-IM-2019-26406, isolate JD133). T. Specimen from Poum, New Caledonia (MNHN-IM-2019-26409, isolate JD128). U. Specimen from Poum, New Caledonia (MNHN-IM-2019-26410, isolate JD137). V. Specimen from Poum, New Caledonia (MNHN-IM-2019-26407, isolate JD130). W. Specimen from Poum, New Caledonia (MNHN-IM-2019-26408, isolate JD119).