Atagema spongiosa (Kelaart, 1858)

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 spongiosa (Kelaart, 1858)

Figs 2A, B , 3A , 4A-C

Doris spongiosa Kelaart, 1858: 97-98. Type locality: Inner Harbor, Trincomalie, Ceylon [= Trincomalee, Sri Lanka].

Doris areolata Alder & Hancock, 1864: 119, pl. 30, figs 1-3 [non Doris areolata Stuwitz, 1835]. Type locality: Waltair, Madras Presidency [= Visakhapatnam, Andhra Pradesh], India.

Phlegmodoris mephitica Bergh, 1878: 594-597, pl. 66, figs 8-20. Type locality: Lapinig Island, Ubay, Philippines.

Trippa (Phlegmodoris) paagoumenei Risbec, 1928: 87-90, text fig. 15, pl. B, fig. 3, pl. 3, fig. 1. Type locality: Paagoumene, New Caledonia.

Material examined.

Pointe Pandop , Koumac, New Caledonia (20°34.9'S, 164°16.6'E), 0 m depth [Koumac 2.1 stn. KM100, rocky shore, rubble, sand, mud, seagrasses], 12 Sep 2018, 1 specimen 49 mm long (MNHN IM-2013-86170, isolate JI02). Koumac, New Caledonia (20°34.7'S, 164°16.5'E), 2-4 m depth [Koumac 2.1 stn. KR231, rocky bottom turning to mud, sponges, Halimeda ], 25 Sep 2018, 1 specimen 27 mm long, dissected (MNHN IM-2013-86190, isolate JI09). Pointe Pandop, Koumac, New Caledonia (20°34.9'S, 164°16.6'E), 0 m depth [Koumac 2.2 stn. KM100, rocky shore, rubble, sand, mud, seagrasses], 1 Mar 2019, 1 specimen 29 mm long (MNHN IM-2013-86188, isolate JI33). Koumac, New Caledonia (20°35.1'S, 164°16.3'E), 7-8 m depth [Koumac 2.2 stn. KR231], 1 Mar 2019, 1 specimen 6 mm long (MNHN IM-2013-86189, isolate JI30) .

Description.

Body oval, flattened, covered with large, rounded tubercles decreasing in size towards the mantle margin (Fig. 2A, B ). A central, longitudinal ridge runs between the rhinophores and gill. A series of depressions on each side of the central ridge, generally decreasing in size towards the mantle margin. Entire dorsal surface, except for the depressions, covered with caryophyllidia. Branchial sheath composed of three large lobes; gill composed of five tripinnate branchial leaves, arranged horizontally in the living animal. Rhinophoral sheaths elevated; rhinophores long, lamellated, with 24 lamellae. Juvenile specimens with less marked dorsal tubercles (Fig. 2B ). Body color opaque greyish brown in adult specimens, except for the depressions, which are dark brown to black (Fig. 2A ); juveniles translucent gray (Fig. 2B ). Rhinophores and branchial leaves are the same color as the dorsum.

Reproductive system (Fig. 3A ) with a long, narrow, simple ampulla that connects with the female gland complex and an elongated, convoluted prostate, with several folds. Prostate ~ 3 × as long as the ampulla. The prostate narrows slightly before expanding into the long, simple, wide deferent duct. Deferent duct several times as wide as the prostate, but shorter in length. The penis is unarmed. The vagina is long and wide, as wide as the deferent duct, and connects directly to the small, oval bursa copulatrix. The small 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 ~ 2 × as large as the seminal receptacle.

Radular formula 18 × 35.0.35 in a 27-mm long specimen (MNHN IM-2013-86190). Rachidian teeth absent. Inner and mid-lateral teeth hamate, having a small cusp and lacking denticles (Fig. 4A, B ). Innermost teeth very small in comparison to mid-laterals (Fig. 4A ). The teeth increase in size suddenly towards the medial portion of the half-row (Fig. 4A ). Outermost teeth small, decreasing in size gradually, and hamate (Fig. 4C ). No jaw was observed, labial cuticle smooth.

Biology.

Geographic range including the Indian and Western Pacific oceans (see synonymy and remarks). In New Caledonia it is found under rocks during the day in shallow water, from 0-8 m depth. The specimens examined were obtained by direct collection during low tide and/or SCUBA diving; they were highly cryptic on rocks covered with sponges and other encrusting organisms.

Remarks.

Doris spongiosa Kelaart, 1858 was originally described from Sri Lanka and re-described by Valdés and Gosliner (2001), who transferred it to the genus Atagema , and recognized two synonyms, Doris areolata Alder & Hancock, 1864 and Phlegmodoris mephitica Bergh, 1878. This species is common across the tropical Indo-Pacific region and is well characterized and illustrated in modern literature ( Wells and Bryce 1993; Yonow 2008; Hervé 2010; Gosliner et al. 2018; Nakano 2018). The specimens here examined from New Caledonia match the original description as well as the common usage of the name in the references above (see Hervé 2010).

Trippa (Phlegmodoris) paagoumenei Risbec, 1928 was originally described based on a single specimen collected in Paagoumene, northern New Caledonia, but it was later reported from Nouméa, southern New Caledonia ( Risbec 1930, 1953). Risbec (1928) described T. paagoumenei as having a rather tough notum, dark violet in color, except towards the edges of the foot and the mantle, where it has a yellowish tint, and completely covered with purplish green, irregular tubercles. One of the specimens from Nouméa was unusual as it was covered by a bright green deposit of metallic appearance ( Risbec 1953). Rudman (2002) considered T. paagoumenei a member of the genus Atagema and a synonym of A. spongiosa , and we concur with this opinion.

Atagema spongiosa is clearly distinct from other species of Atagema recognized as valid in the modern literature, such as Atagema ornata (Ehrenberg, 1831) [= Atagema intecta Kelaart, 1858] and Atagema carinata (Quoy & Gaimard, 1832), illustrated and/or redescribed in Willan and Coleman (1984), Valdés and Gosliner (2001), and Rudman (2005), as well as Atagema echinata (Pease, 1860), illustrated by Tibiriçá et al. (2017) and Gosliner et al. (2018). None of these species possesses the characteristic dorsal pattern of tubercles, depressions with a central ridge present in A. spongiosa . Atagema boucheti Valdés & Gosliner, 2001, described based in a preserved specimen from New Caledonia deep water (405-411 m depth), is characterized by having the dorsum covered by large, irregularly scattered tubercles, not aligned to form ridges. Although the live color of this species is unknown, the external morphology is clearly different from other species of Atagema including Atagema spongiosa (see Valdés and Gosliner 2001).

Figures

Figure 2. Photographs of live animals of the genus Atagema Gray, 1850 A, B Atagema spongiosa (Kelaart, 1858), MNHN IM- 2013 - 86188 on black background (A), MNHN IM- 2013 - 86189 in situ (B) C, D Atagema kimberlyae sp. nov., MNHN IM- 2013 - 86191 on black background (C), MNHN IM- 2013 - 86191 in situ (D) E Atagema papillosa (Risbec, 1928), MNHN IM- 2013 - 86192 on black background.

Figure 3. Drawings of the reproductive systems of specimens of the genus Atagema Gray, 1850 A Atagema spongiosa (Kelaart, 1858), MNHN IM- 2013 - 86190 B, C Atagema kimberlyae sp. nov., MNHN IM- 2013 - 86191, general view (B), detail of the bursa copulatrix and seminal receptable (C) D, E Atagema papillosa (Risbec, 1928), MNHN IM- 2013 - 86192, general view (D), detail of the bursa copulatrix and seminal receptable (E). Abbreviations: am, ampulla; bc, bursa copulatrix; dd, deferent duct; fg, female gland complex; pr, prostate; sr, seminal receptacle; vg, vagina.

Figure 4. SEM of the radula of specimens of the genus Atagema Gray, 1850 A-C Atagema spongiosa (Kelaart, 1858), MNHN IM- 2013 - 86190, innermost teeth (A), mid-lateral teeth (B), outer lateral teeth (C) D-F Atagema kimberlyae sp. nov., MNHN IM- 2013 - 86191, innermost teeth (D), mid-lateral teeth (E), outer lateral teeth (F) G-I Atagema papillosa (Risbec, 1928), MNHN IM- 2013 - 86192, innermost teeth (G), mid-lateral teeth (H), outer lateral teeth (I).