Hyalorisia solomonensis Fassio, Bouchet & Oliverio new species

MOTU-9 (Figs 3K, 6C, 7I, R)

Type material: Holotype: off Santa Isabel, Solomon Islands, SALOMON 2, Stn CP2186, 08°17 S, 160°00 E, 487–541 m, MNHN-IM-2007-34203 (male).

Material examined: Holotype and other material (MNHN-IM-2007-34215, MNHN-IM-2007-34216, MNHN-IM-2007-34217 and MNHN-IM-2013-66982).

Etymology: From the general area of the type locality, Solomon Islands.

ZooBank registration: urn:lsid:zoobank.org:act: 65270D2E-622E-461A-BF55-C01018FA7F6E.

COI-based diagnosis: Six diagnostic (autapomorphic) positions in the alignment: 347(C), 373(G), 535(G), 542(C), 544(G) and 553(T).

Shell (data for holotype shown within parentheses): Size small to medium for genus: length 4.5–9 (8) mm, width 3–6 (5) mm, height 1–2 (2) mm; ellipsoidal or ovoidal, depressed; white shell surface with smooth yellowish periostracum; anterior margin rounded; protoconch of 1–1.2 (1.1) whorls, diameter of nucleus 0.08–0.1 (0.08) mm; teleoconch smooth except for distinct commarginal growth ridges; apertural margin thin, interior glossy white; lamella narrow to wide, width 0.23–0.69 (0.69) mm.

Soft parts (ethanol preserved): Head completely whitish or grey at the base; cephalic tentacles whitish with grey base; pseudoproboscis whitish, mantle grey with whitish border.

Radula: Taenioglossate, 2-1-R-1-2; marginal teeth sickle shaped; internal marginals with few denticles on the inner edge; lateral teeth triangular, highly denticulated on outer edge, inner edge denticulation variable; rachidian tooth triangular, highly denticulated on both edges.

Host: No records available of direct collection from host. Two specimens of P. caducum (MNHN-IM-2007-33865 and MNHN-IM-2007-33866) were found at the same stations and showed marks on the shells corresponding to the contour of the Hyalorisia specimens (MNHN-IM-2007-34216 and MNHN-IM-2007-34217). The holotype was found at a station where the only propeamussiids found were P. caducum and P. investigatoris . Another specimen (MNHN-IM-2007-34215) was found at a station where the only propeamussiid found was P. caducum .

Distribution: So far known only from the Solomon Islands and Papua New Guinea, at depths of 510– 520 m.

Remarks: Hyalorisia solomonensis n. sp. was found sympatrically with H. melanesica n. sp. (MOTU-8) in Ainto Bay, New Britain, Papua New Guinea (Solomon Sea).