Rissoella diaphana

(Alder, 1848)

Description (shell):
Shell small, transparent, smooth, fragile; four-and-one-half tumid whorls, slightly stepped at sutures; apex blunt. Last whorl about 70 % of shell height. Sculpture of prosocline growth lines. Aperture egg-shaped; inner lip slightly reflected over small umbilical chink.

Up to 1.5 x 0.9 mm.


Snout deeply bifid, appearance tentaculate; cephalic tentacles cylindrical, finely setose. Mantle edge without pallial tentacles. Foot with anterior pedal gland opening dorsally and posterior gland opening ventrally, latter linked by a groove to posterior margin of sole. Colour: cream with some darker patches. Operculum horny, nucleus close to columellar margin.

Common in summer among filamentous red algae and in coralline rock-pools between MTL and LWST.

Distributed from Mediterranean to Norway; absent from Baltic and most of North Sea (Distr. R. diaphana).