Hyalorisia lehibe Fassio, Bouchet & Oliverio new species

MOTU-5 (Figs 3E, 5A)

Type material: Holotype: off Mahajanga, NW Madagascar, MIRIKY, Stn CP3253, 15°25 S, 45°55 E, 943–950 m, MNHN-IM-2007-39212. One paratype: same locality as holotype, MNHN-IM-2007-39206.

Etymology: After the Malagasy adjective ‘lehibe’, meaning ‘big or large’, referring to the size of this species.

ZooBank registration: urn:lsid:zoobank.org:act: FCF15E07-177B-4E13-B2DF-0DD8E9261DC8.

COI-based diagnosis: Four diagnostic (autapomorphic) positions were scored in the alignment: 157(C), 292(G), 469(G) and 631(G).

Shell (data for holotype shown within parentheses): Medium sized for the genus: length 15–17 (15) mm, width 12.5–14.5 (12.5) mm, height 4–5 (4) mm; thin, rounded, depressed; white shell surface with smooth yellowish periostracum; anterior margin slightly angled; protoconch (intact only in holotype) of 1.1 whorls, diameter of nucleus 0.13 mm; teleoconch smooth except for distinct commarginal growth ridges; apertural margin thin, interior glossy white; lamella wide, width 1.8–2.48 (1.8) mm.

Soft parts: Not examined; damaged due to tissue clipping.

Host: The holotype was found attached to P. watsoni (MNHN-IM-2007-39211). The paratype (MNHN-IM-2007-39206) was found at the same station and has a registration number that is close to those of two specimens of P. watsoni (MNHN-IM-2007- 39209 and MNHN-IM-2007-39210); the shells of both bivalves bear a mark that corresponds to the contour of the Hyalorisia specimen.

Distribution: So far known only from the Madagascar side of the Mozambique Channel, at depths of 943– 950 m.

Remarks: Hyalorisia lehibe n. sp. was found off Mahajanga, NW Madagascar, where it occurred sympatrically with H. madagascarensis n. sp. (MOTU-10) and H. kely n. sp. (MOTU-7).