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(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).

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

Colour:
Translucent white.

Animal:
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).

Habitat:
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.

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

Retusa obtusa