Atagema sobanovae, 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

Atagema sobanovae sp. nov.

Figs 5 , 6 , 7

Atagema ? Atagema sp. 9: Gosliner et al. 2018: 116.

Type material.

Holotype: Koumac, New Caledonia (20°35.6'S, 164°16.3'E), 3 m depth [Koumac 2.1 stn. KR230], 28 Sep 2018, 22 mm long (MNHN IM-2013-86211, isolate JI16).

Other material examined.

Cap Deverd , Koumac, New Caledonia (20°46.2'S, 164°22.6'E), 5 m [Koumac 2.1 stn. KR213], 12 Sep 2018, 1 specimen 13 mm long (MNHN IM-2013-86178, isolate JI06). Koumac, New Caledonia (20°39.6'S, 164°16.2'E), 6 m depth [Koumac 2.1 stn. KR229], 27 Sep 2018, 1 specimen 8 mm long (MNHN IM-2013-86175, isolate JI28). Koumac, New Caledonia (20°35.6'S, 164°16.3'E), 3 m depth [Koumac 2.1 stn. KR230], 28 Sep 2018, 1 specimen 17 mm long, dissected (MNHN IM-2013-86180, isolate JI23); 1 specimen 18 mm long, dissected (MNHN IM-2013-86179, isolate JI21). Koumac, New Caledonia (20°35.1'S, 164°16.3'E), 7 m depth [Koumac 2.1 stn. KR409, muddy bottom with solitary soft and hard corals and hydroids], 28 Sep 2018, 1 specimen 8 mm long (MNHN IM-2013-86229). Koumac, New Caledonia (20°35.1'S, 164°16.3'E), 3 m [Koumac 2.2 stn. KR231], 1 Mar 2019, 1 specimen 9 mm long (MNHN IM-2013-86176, isolate JI44). Koumac, New Caledonia (20°37.3'S, 164°18'E), 6 m depth [Koumac 2.3 stn. KD522, grey sand with Caulerpa and Halimeda ], 2 Nov 2019, 1 specimen 10 mm long (MNHN IM-2013-86174, isolate JI19). Koumac, New Caledonia (20°34.3'S, 164°13.5'E), 1-10 m depth [Koumac 2.3 stn. KR907, sanded slab with gorgonians, scattered seagrass, and Caulerpa ; channel drop-off with gorgonians], 7 Nov 2019, 1 specimen 7 mm long (MNHN IM-2013-86173, isolate JI41). Koumac, New Caledonia (20°34.4'S, 164°13.8'E), 8 m depth [Koumac 2.3 stn. KR913], 14 Nov 2019, 1 specimen 11 mm long (MNHN IM-2013-86171, isolate JI29); 1 specimen 10 mm long (MNHN IM-2013-86172, isolate JI46). Koumac, New Caledonia (20°35.1'S, 164°16.3'E), 7 m depth [Koumac 2.3 stn. KR1019, "fond de vase" with Caulerpa and sponges], 4 Nov 2019, 1 specimen 28 mm long (MNHN IM-2013-86181, isolate JI05); 1 specimen 22 mm long, dissected (MNHN IM-2013-86187, isolate JI08); 1 specimen 9 mm long (MNHN IM-2013-86177, isolate JI45) .

Description.

Body oval, elevated, completely covered with a dense, complex network of delicate ridges (Fig. 5 ). Large caryophyllidia present at the points where ridges meet. A series of small depressions free of ridges and caryophyllidia present on each side of the mantle. A single, elevate dorsal hump present on the center of the dorsum, not visible in juvenile specimens (Fig. 5E ). Branchial sheath composed of three lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 8-10 lamellae. Body color opaque creamy grey, depressions a bit darker. Rhinophores and branchial leaves are the same color as the dorsum.

Reproductive system (Fig. 6 ) with a short, convoluted ampulla that connects with the female gland complex and an elongated prostate. The prostate is as long as the ampulla and it narrows slightly into an elongate duct before expanding into the short, simple, deferent duct. The penis is unarmed. The vagina is short and wide, approximately as wide as the deferent duct, and connects directly to the oval bursa copulatrix. The oval seminal receptacle also connects to the bursa copulatrix next to the vaginal opening and the short uterine duct that enters the female gland complex. The bursa copulatrix is slightly larger than the seminal receptable.

Radular formula 22 × 35.0.35 in an 18-mm long specimen (MNHN IM-2013-86179) and 17 × 34.0.34 in a 22-mm long specimen (MNHN IM-2013-86187). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a small cusp and lacking denticles (Fig. 7A, B ). Innermost teeth very small in comparison to mid-laterals (Fig. 7A ). The teeth increase in size gradually towards the medial portion of the half-row (Fig. 7A ). Outermost teeth small, decreasing in size gradually, and hamate (Fig. 7C ). No jaw was observed, labial cuticle smooth.

Biology.

This species could be widespread in the Western Pacific (see remarks). Found in shallow water (1-10 m depth). The specimens were exclusively collected on an unidentified species of grey sponge inhabiting the surface of scallops; the nudibranchs were highly cryptic on the sponge and often found buried in the sponge tissue. Few specimens were obtained by direct collection while SCUBA diving but more of them were found in the lab while searching for crustaceans associated with the sponges.

Etymology.

This species is named after Anna Šobáňová, crustacean expert who originally discovered this species in the field while looking for crustaceans living in sponges.

Remarks.

Atagema sobanovae sp. nov. is assigned to the genus because of its position in the molecular phylogenetic trees, in a clade containing other species of Atagema such as A. spongiosa and A. cf. osseosa . Also, the morphological characteristics of this new species are consistent with the diagnosis of the genus by Valdés and Gosliner (2001). Atagema sobanovae sp. nov. has a flexible body with series of dorsal ridges and a central conspicuous tubercle, all covered with caryophyllidia, the anterior border of the branchial sheath is composed of three lobes and the gill is arranged horizontally; the prostate is tubular, with a single portion, the penis and vagina are unarmed; the labial cuticle smooth and all radular teeth are hamate and smooth.

A review of the literature shows that no other described species of Atagema possesses the external characteristics of A. sobanovae sp. nov. The only other tropical Indo-Pacific species with a uniform color is Atagema carinata (Quoy & Gaimard, 1832), which was described from the coast of Thames, New Zealand, as yellowish white with a dorsal longitudinal ridge between the rhinophores and the gill. The illustration provided by Quoy and Gaimard (1832-1833: pl. 16, figs 10-14) represents an animal with a distinct dorsal ridge very different from the complex dorsal pattern of A. sobanovae sp. nov. with depressions, ridges, and a central tubercle. The specimens of A. carinata described and illustrated by Rudman (2005) are consistent with the original description.

A specimen from the Philippines illustrated by Gosliner et al. (2018) as Atagema sp. 9 could belong to A. sobanovae sp. nov. but this needs anatomical and molecular confirmation.

Figures

Figure 5. Photographs of live animals of Atagema sobanovae sp. nov. A, B MNHN IM- 2013 - 86180, on black background (A), in situ (B) C, D holotype (MNHN IM- 2013 - 86211), on black background (A), in situ (B) E MNHN IM- 2013 - 86229 juvenile specimen on black background.

Figure 6. Drawing of the reproductive system of Atagema sobanovae sp. nov., MNHN IM- 2013 - 86180. Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; fg, female gland complex; pr, prostate; sr, seminal receptacle; vg, vagina.

Figure 7. SEM of the radula of specimens of Atagema sobanovae sp. nov., MNHN IM- 2013 - 86179, innermost teeth (A), mid-lateral teeth (B), outer lateral teeth (C).