Retusa sp. 4

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 742-743

Retusa sp. 4

Figs 77C, D, 78

MATERIAL EXAMINED. — New Caledonia proper. BIOGEOCAL: stn KG 278, 22°48’S, 166°20’E, 2250 m, 1 dd .

DISTRIBUTION. — Single specimen collected from the New Caledonia area (Fig. 78), in 2250 m .

DESCRIPTION. — Shell morphology. Length 4 mm, width 2 mm (single specimen examined). Shell fragile, oval to elongate, with nearly parallel sides (Fig. 77C). Only 1 whorl visible, forming nearly the entire shell, except for the top of the spire, where 3 whorls are visible. Apex flat, slightly convex, not umbilicate (Fig. 77D). Protoconch unknown. Anterior end of the shell rounded. Aperture just slightly shorter than the shell, wider anteriorly and narrowing gradually at about 1/3 of its length. Columellar margin slightly thickened. Columella simple, with no folds. Umbilicus closed. No sculpture. Colour uniformly translucent whitish.

Anatomy. Unknown. The single shell collected lacked soft parts.

REMARKS. — Retusa sp. 4 is very similar to Retusa diaphana n. sp. in shell morphology, but can be distinguished by its more elongate shell and shorter aperture. Tornatina ovalis Thiele, 1925 , described from shallow waters in Sumatra, Indonesia, is also similar to Retusa sp. 4 but it has a more elongate spire and a conspicuous denticle on the columella. Also, the protoconch of T. ovalis is typical of the genus Acteocina and future revision should transfer it to this genus.

This species is placed in Retusa , pending availability of complete specimens.