Hyalorisia profunda Fassio, Bouchet & Oliverio new species

MOTU-9 (Figs 3I, 6A)

Type material: Holotype: South China Sea, ZHONGSHA 2015, Stn CP4137, 19°53 N, 114°25 E, 524–536 m, MNHN-IM-2013-59695. One paratype: same locality as holotype, MNHN-IM-2013-59696.

Material examined: Type and other material (MNHN-IM-2007-33806, MNHN-IM-2007-33828 and MNHN-IM-2013-44655).

Etymology: After the Latin adjective profundus, -a, -um, meaning deep, with reference to the fact that this species occurs at great depths.

ZooBank registration: urn:lsid:zoobank.org:act: 668C5D77-6FAB-457D-A7D9-0F142DC12E49.

COI-based diagnosis: Three diagnostic (autapomorphic) positions in the alignment: 52(G), 325(T) and 359(C).

Shell (data for holotype shown within parentheses): Size small to medium for the genus: length 6–9 (7) mm, width 4–6 (5) mm, height 2–3 (2) mm; thin, ellipsoidal to rounded, depressed; white shell surface with smooth yellowish periostracum; anterior margin rounded; protoconch of 1–1.1 (1.1) whorls, diameter of nucleus 0.1–0.21 (0.16) mm; teleoconch smooth except for distinct commarginal growth ridges; apertural margin thin, interior glossy white; lamella narrow, width 0.29–0.69 (0.4) mm.

Soft parts: Not examined; damaged by tissue clipping.

Host: Based on the field label, the holotype and paratype were attached to a Propeamussium sp.; at that station, the only propeamussiids collected were P. jeffreysii and P. caducum . Two specimens (MNHN-IM-2007-33806 and MNHN-IM-2007-33828) were found at the same station; these and specimens of P. caducum (MNHN-IM-2007-33805 and MNHN-IM-2007-33827, respectively) have consecutive registration numbers, and MNHN-IM-2007-33827 also has a mark on the shell that corresponds to the contour of the Hyalorisia specimen. Another Hyalorisia specimen (MNHN-IM-2013-44655) was found at a station where the only propeamussiid collected was P. caducum .

Distribution: So far known only from the South China Sea and the Philippines, at depths of 536–1,240 m.

Remarks: Hyalorisia profunda n. sp. was found syntopically with H. nanhaiensis n. sp. (MOTU-6) on the continental slope of the South China Sea (ZHONGSHA 2015: Stn CP4137).