Gymnodoris suggens ( Risbec, 1928 )

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 : 34-35

Gymnodoris suggens ( Risbec, 1928)

( Figs. 6C–K )

Trevelyana suggens Risbec, 1928: 190–193 , text fig. 58, text pl. B, fig. 1 [p. 213], pl. 5, fig. 3. pl. 5, fig. 6. Type locality: Several localities including Nouméa, New Caledonia, Port Despointes, New Caledonia, and Tembia, New Caledonia.

Material examined. 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 5 mm preserved length (MNHN-IM-2019-26509, isolate JD135) . New Caledonia: North Province: Poum, East Ilôt Baaba ( 20°2.92'S, 163°59.87'E), 0 m depth [ABC Poum Expedition, stn. ABC47, intertidal], 18 Jun 2023, 1 specimen 6 mm preserved length (MNHN-IM-2019-26512, isolate JD138) . New Caledonia: North Province: Poum, Baie Tiêêlé ( 20°2.92'S, 163°49.61'E), 0 m depth [ABC Poum Expedition, stn. ABC53 ], 19 Jun 2023, 1 specimen 4 mm preserved length (MNHN-IM-2019-26456, isolate JD105); 1 specimen 3 mm preserved length (MNHN-IM-2019-26508, not sequenced) . New Caledonia: North Province: Poum, South Ilôt Yandé ( 20°4.57'S, 163°49.59'E), 0 m depth [ABC Poum Expedition, stn. ABC58 ], 20 Jun 2023, 1 specimen 3 mm preserved length (MNHN-IM-2019-26455, isolate JD100) . New Caledonia: North

Province: Poum, South West of Baaba ( 20°4.09'S, 163°57.09'E), 0 m depth [ABC Poum Expedition, stn. ABC 68], 21 Jun 2023, 1 specimen 4 mm preserved length (MNHN-IM-2019-26505, isolate JD107). New Caledonia: North Province: Poum, Paabö , Baaba Is.,( 20°3.12'S, 163°59.84'E), 0 m depth [ABC Poum Expedition, stn. ABC85 ], 23 Jun 2023, 1 specimen 4 mm preserved length (MNHN-IM-2019-26510, isolate JD134) . 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 4 mm preserved length (MNHN-IM-2019-26520, isolate JD132) . New Caledonia: South Province: Mont Dore, Baie Uie ( 22°20.6'S, 166°43.3'E), 3 m depth, 10 Sep 2023, 1 specimen 4 mm preserved length [rocky coastal area] (MNHN-IM-2019-26513, not sequenced), leg. Y. Thévenet.

Description. Body narrow, elongate, smooth, lacking tubercles ( Figs. 6C–L ). Velum distinct, with few irregular tubercles; notal rim absent, velum merges into notum. Posterior end of foot tapering into narrow, long “tail.” Color translucent white, with numerous oval yellow or orange spots, large irregular opaque white patch anterior to gill, smaller opaque white, diamond-shaped patch posterior to rhinophores. Some specimens with minute brown spots all over dorsum. Internal organs visible through body wall as brown, white, sometimes orange areas. Posterior end of foot translucent grey with a network of glandular structures visible through body wall. Rhinophores very elongated, tentacular, with 8 lamellae, translucent white stalk, brownish-grey club, with yellow or orange tips. Gill with 15–17 small, simple leaves, arranged in a circle around anus. Gill leaves translucent with yellow tips, opaque white base. Foot narrower than notum, opaque white. Oral tentacles absent.

Phylogenetic position. Gymnodoris suggens is a well-supported monophyletic group (PP: 1, MLB: 100), sister to the undescribed species G. sp. L (PP: 0.99, MLB: 74) and part of a larger clade (PP: 1, MLB: 99) also including G. sp. M and G. sp. N ( Fig. 1A ).

Remarks. Risbec (1928) originally described Trevelyana suggens based on several specimens collected from various localities in New Caledonia. The animals were described as bilobed anteriorly, with a smooth, whitish transparent body having rounded yellow spots, and the digestive gland visible through the notum as blackish area and a reddish genital area. The gill leaves were described as shaped like transparent radiating blades with a yellow spot at their top. Risbec (1928: pl. 5, figs. 3, 6) also illustrated a white patch anterior to the gill of some specimens. This description matches perfectly with the characteristics of the specimens here examined from New Caledonia, which are confidently assigned to this species. A specimen illustrated by Risbec (1928: pl. 7, fig. 10) as “ Trevelyana suggens varieté” has a different color pattern and probably belongs to a different, undetermined species.

Gymnodoris sp. L (illustrated by Knutson & Gosliner, 2022) is externally very similar to Gymnodoris suggens but appears to be genetically different. Other Indo-Pacific records of similarly colored animals include Japan and Papua New Guinea as Gymnodoris sp. 27 ( Nakano, 2018) and Gymnodoris sp. 21 ( Gosliner et al., 2018), as well as South Korea as Gymnodoris sp. ( Koh, 2006). It is unclear if those records correspond to G. suggens or a species complex also including G. sp. L.

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 6. Gymnodoris striata (Eliot, 1908), Gymnodoris suggens (Risbec, 1928), and Gymnodoris okinawae Baba, 1936, photographs of live animals showing color variation. A. G. striata, specimen from New Caledonia: Loyalty Is.: Ouvéa, (MNHN- IM-2019-26449, isolate JD165). B. G. striata, specimen fromNew Caledonia: Loyalty Is.: Ouvéa, (MNHN-IM-2019-26448, isolate JD182). C. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26455, isolate JD100). D. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26456, isolate JD105). E. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26505, isolate JD107). F. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019- 26520), isolate JD132). G. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26512, isolate JD138) H. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26510, isolate JD134). I. G. suggens, specimen from Poum, New Caledonia (MNHN-IM-2019-26509), isolate JD135). J. G. suggens, specimen from Poum, New Caledonia (MNHN-IM- 2019-26508, not sequenced). K. G. suggens, specimen from Mont Dore, New Caledonia, photo Y. Thévenet (MNHN-IM-2019- 26513, not sequenced). L. G. okinawae, specimen from Ouaième, New Caledonia (MNHN-IM-2019-26528, isolate JD178), photo A. Doulas. M. G. okinawae, specimen from Nouméa, New Caledonia (MNHN-IM-2019-26450, isolate JD168).