Retusa obtusa

(Montagu, 1803)

Description (shell):
Shell fragile, glossy, and sculptured; variable in shape, usually elongated, not rounded like Acteon tornatilis . Aperture usually smaller than last whorl; spire may or may not be present (R. obtusa).

Up to 10 mm. Total length (including animal) up to 15 mm.

Translucent white.

Body whitish, extending beyond shell only anteriorly. Cephalic shield square, slightly indented in midline anteriorly; posteriorly, two rounded tentacles point backwards and outwards. Foot very small, squat, shield-like shape in ventral view, approximately same size as head, indented anteriorly (R. obtusa-drawing).

Burrower in mud or muddy sand, living below the surface in the first few centimetres, and feeds on Hydrobia ulvae . It can be found by sieving the mud; in finer substrata, the flat-topped variety pertenuis only reaches 3 mm in length. Occurs from lower shore to 300 m.

Generally distributed in the North Sea. Locally abundant in favourable localities. (Distr. R. obtusa).