Rissoella opalina

(Jeffreys, 1848)

Description (shell):
Shell small, semi-transparent, smooth; globular, with three or four tumid, rapidly expanding whorls; sutures deep. Aperture almost D-shaped, columella nearly straight, with a thickened peristome and a small umbilical chink.

Up to 2 x 1.4 mm.

Pale yellow or horn coloured, with opalescent lustre; three dark spots on mantle show through in living shells.

Body similar to Rissoella diaphana . Snout bifid, slightly lobed; cephalic tentacles bifid, setose.

Locally common in summer on filamentous red algae and in rock-pools near LWST; often with Rissoella diaphana .

Distributed along western shores of British Isles from Channel Isles to Shetland; absent from North Sea coasts, east Channel, and Baltic (Distr. R. opalina).