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Cetoconcha gigas sp. nov. (Fig. 9A–G) urn:lsid:zoobank.org:act: 16332040-0DB3-48EF-8B00- 111A3DC37417 Pholadomya cf. adelaidis Hedley 1916 — Mühlenhard-Siegel 1989: 167, fig. 44. Poromya spinulosa (non Ŋiele 1912)— Engl 2012: 64, pl. 13, fig. 4c. Type material: Holotype: USNM 904483 , one individual. Paratype: USNM 1283153, one individual. Type locality: Zavodovski Island, SW of island, South Sandwich Islands, Scotia Sea (56°19.8 ʹ S 27°38.4 ʹ W), 575 m. Etymology: Ŋe name gigas in Latin means giant and refers to the large size of the species within the genus. Distribution New records: South Sandwich Island and off West Antarctic Peninsula. Literature records: Off Elephant Island as Pholadomya cf. adelaidis (Mühlenkardt-Siegel 1989) and Weddell Sea as Poromya spinulosa (Engl 2012). Bathymetry: 278–575 m. Material examined: 65°39 ʹ 36″S, 68°04 ʹ 48″W, 278 m (USNM 1283153) one individual (paratypes). Diagnosis Shell elongated, ≤ 61 mm long; ornamented with ≤90 weak, closely spaced radial lines. Hinge of right valve with obsolete cardinal tooth; less valve with a longitudinal ridge near end of posterodorsal margin. Siphons surrounded by 19 siphonal tentacles. Description Shell large in size (≤ 61 mm L), thin, ovate, elongated, inequilateral. Surface with ~90 weak, closely spaced radial lines interspaced by groups of four to eight cylindrical granules, usually covered by debris, and commarginal growth lines. Periostracum brownish. Umbo subcentral (displaced anteriorly) and prosogyrus. Antero- and posterodorsal margin gently descendent. Anterior margin rounded, posterior rounded to acute. Ventral margin widely curved. Right cardinal tooth weak, obsolete, fiưing in a small socket in less valve. Less valve with elongated longitudinal ridge near end of posterodorsal margin. Resilifer opisthodetic. Interior iridescent, with numerous closely spaced radial lines not corresponding to external lines. Adductor muscle scars well marked, anterior larger than posterior. Longitudinal scar marking insertion of ... |