Crenella decussata

(Montagu, 1808)

Description (shell):
Shell oval, tumid; almost equilateral, umbones more or less on midline with beaks curving anteriorly. Sculpture of numerous radiating ribs, extending over whole shell surface, intersecting with equally numerous concentric lines, giving a finely decussate appearance; prodissoconch apparently smooth, with exceptionally fine sculpture. Growth stages clear, but not prominent. External sculpture visible on inner surface, adductor scars indistinct. Margin crenulate, crenulations extending along hinge line and resembling small teeth, developed below umbo as small, grooved callus.

Up to 3 mm in length.

Shell white, periostracum light yellow. Inner surface white or brown.

The mantle forms only one very short siphon. The animal gets rid of waste through this siphon, while fresh supplies are being taken in by the open front. The foot consists of a cylindrical stalk and a tongue-shaped expansion which is used for crawling. These animals are very active, and like to climb and hang suspended by means of a single thread.

Offshore, on sand and fine gravel.

Reported from the Bristol Channel northwards, absent from the south coasts of the British Isles (Distr. C. decussata).