Rostanga poddubetskaiae, Innabi & Stout & Valdés, 2023

Innabi, Julie, Stout, Carla C. & Valdes, Angel, 2023, Seven new " cryptic " species of Discodorididae (Mollusca, Gastropoda, Nudibranchia) from New Caledonia, ZooKeys 1152, pp. 45-95 : 45

Rostanga poddubetskaiae sp. nov.

Figs 11 , 12 , 13

Type material.

Holotype: Anse de Koumac, Koumac, New Caledonia (20°34'S, 164°16'E), 4 m depth [Koumac 2.1 stn. KR206], 5 Sep 2018, 1 specimen 23 mm long (MNHN IM-2013-86199, isolate JI01).

Other material examined.

Anse de Koumac, Koumac, New Caledonia (20°34'S, 164°16'E), 4 m depth [Koumac 2.1 stn. KR206], 5 Sep 2018, 1 specimen 25 mm long (MNHN IM-2013-86200, isolate JI17); 1 specimen 12 mm long (MNHN IM-2013-86201, isolate JI32); 1 specimen 26 mm long, dissected (MNHN IM-2013-86202, isolate JI03); 1 specimen 19 mm long, dissected (MNHN IM-2013-86203, isolate JI12); 1 specimen 16 mm long, dissected (MNHN IM-2013-86204, isolate JI20). Cap Deverd , Koumac, New Caledonia (20°46.2'S, 164°22.6'E), 5 m depth [Koumac 2.1 stn. KR213] , 29 Sep 2018, 1 specimen 26 mm long, dissected (MNHN IM-2013-86205, isolate JI27); 1 specimen 28 mm long, dissected (MNHN IM-2013-86206, isolate JI13). Anse de Koumac , Koumac, New Caledonia (20°34.6'S, 164°16.1'E), 5 m depth [Koumac 2.1 stn. KR219] , 17 Sep 2018, 1 specimen 12 mm long (MNHN IM-2013-86207, isolate JI39); 1 specimen 23 mm long, dissected (MNHN IM-2013-86208, isolate JI25); 1 specimen 26 mm long (MNHN IM-2013-86209, isolate JI18); 1 specimen 17 mm long (MNHN IM-2013-86210, isolate JI40). Koumac , New Caledonia (20°35.6'S, 164°16.3'E), 3 m depth [Koumac 2.2 stn. KR230] , 2 Mar 2019, 1 specimen 20 mm long (MNHN IM-2013-86213, isolate JI36); 2 Mar 2019, 1 specimen 21 mm long (MNHN IM-2013-86214, isolate JI37); 3 Mar 2019, 1 specimen 20 mm long (MNHN IM-2013-86212, isolate JI31). Pointe de Pandop , Koumac, New Caledonia (20°34.9'S, 164°16.5'E), 7 m depth [Koumac 2.1 stn. KR868] , 26 Sep 2018, 1 specimen 26 mm long (MNHN IM-2013-86215, isolate JI15); 1 specimen 24 mm long (MNHN IM-2013-86216, isolate JI24); 1 specimen 14 mm long (MNHN IM-2013-86217, isolate JI38). Koumac , New Caledonia (20°33.7'S, 164°13.1'E), 12 m depth [Koumac 2.3 stn. KR206] , 3 Nov 2019, 1 specimen 19 mm long (MNHN IM-2013-86218, isolate JI07).

Description.

Body oval, elongate, completely covered with numerous caryophyllidia (Fig. 11 ). Branchial and rhinophoral sheaths low, simple, circular; gill composed of seven wide, tripinnate branchial leaves, extended laterally, lying on the dorsum in the living animal. A low, irregular, inconspicuous ridge runs between the rhinophores and the gill, not clearly visible in all specimens. Rhinophores very elongate, almost conical, lamellated, with 15 or 16 lamellae. Body color pinkish to orange, with irregular darker patches all over the dorsum. Rhinophores reddish; branchial leaves the same color as the dorsum.

Reproductive system (Fig. 12 ) with a long, narrow, curved ampulla that connects with the female gland complex and an irregular, elongate prostate. The prostate is wider than the ampulla, but it narrows substantially into a long, folded tube, before expanding into the short, wide deferent duct. The penis is unarmed. The vagina is elongate, several times narrower than the deferent duct, connecting directly to the large, oval bursa copulatrix. The smaller, elongate seminal receptacle also connects to the bursa copulatrix next to the vaginal connection, and the short uterine duct that enters the female gland complex. The bursa copulatrix is several times larger than the seminal receptacle.

Radular formula 28 × 73.0.73 in a 23-mm long specimen (MNHN IM-2013-86208), 36 × 80.0.80 in a 26-mm long specimen (MNHN IM-2013-86205), and 37 × 81.0.81 in a 26-mm long (MNHN IM-2013-86209). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a small cusp and lacking denticles (Fig. 13A, B ). Innermost teeth very small in comparison to mid-laterals (Fig. 13A ). The teeth increase in size gradually towards the medial portion of the half-row (Fig. 13B ). Outermost teeth small, decreasing in size gradually, and hamate (Fig. 13C ), outermost one with 13-20 irregular denticles. No jaw was observed, labial cuticle smooth.

Biology.

All the specimens were found on an unidentified species of sponge while SCUBA diving. The presence of these highly cryptic nudibranchs was initially determined in the field by observing the egg masses on the sponges. In most cases, to separate the nudibranchs, the sponges were brought to the lab and examined under a microscope.

Etymology.

This species is named after Marina Poddubetskaia, indefatigable collector and diver, who first discovered the animals here described during the two of the Koumac expeditions.

Remarks.

Rostanga poddubetskaiae sp. nov. is provisionally assigned to the genus Rostanga based on the results of the molecular phylogenetic analyses, which place this species solidly nested within a clade containing other species identified as members of Rostanga . However, there are some notable differences between Rostanga poddubetskaiae sp. nov. and the diagnoses of the genus Rostanga provided by Rudman and Avern (1989) and Valdés and Gosliner (2001), such as the absence of jaws and elongate outermost radular teeth, and the presence of short caryophyllidia; moreover, the arrangement of the branchial leaves flattened against the dorsum and the presence of a dorsal ridge are unusual for a species of Rostanga . Additional resolution in the phylogeny of dorid nudibranchs and a larger sample are needed before this species can be placed in a genus with confidence.

Rostanga poddubetskaiae sp. nov. appears to be sister to Rostanga elandsia Garovoy, Valdés & Gosliner, 2001 from South Africa, but additional species need to be included in the analysis to confirm those relationships. Morphologically, R. poddubetskaiae sp. nov. exhibits a number of differences from other members of this genus, including the presence of a dorsal ridge, elongate rhinophores, a gill flattened against the body, and smooth, hamate inner and mid radular teeth, and short, pectinate outermost lateral teeth. The Indo-Pacific species of Rostanga have been reviewed in papers by Rudman and Avern (1989), Baba (1991), and Garovoy et al. (2001), and none of them have external and internal characteristics present in R. poddubetskaiae sp. nov. The only exception is Rostanga crawfordi (Burn, 1969), described as Rostanga australis Rudman & Avern, 1989, which appears to have a dorsal ridge in some specimens (see Rudman and Avern 1989; Coleman 2008) and a similar external coloration to R. poddubetskaiae sp. nov., but the radular teeth are very different: specifically, the outer teeth are elongate with numerous denticles on the tip.

Figures

Figure 11. Photographs of live animals of Rostanga poddubetskaiae sp. nov. A holotype MNHN IM- 2013 - 86199 on black background B holotype (MNHN IM- 2013 - 86199) and MNHN IM- 2013 - 86217 in situ with egg masses C MNHN IM- 2013 - 86205 in situ D MNHN IM- 2013 - 86216 and MNHN IM- 2013 - 86217 in situ E MNHN IM- 2013 - 86209 on black background.

Figure 12. Drawing of the reproductive system of Rostanga poddubetskaiae sp. nov., MNHN IM- 2013 - 86202. Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; fg, female gland complex; pr, prostate; sr, seminal receptacle; vg, vagina.

Figure 13. SEM of the radula of specimens of Rostanga poddubetskaiae sp. nov., MNHN IM- 2013 - 86205 A innermost teeth B mid-lateral teeth C outer lateral teeth.