Cockle

Cockle (Cardium), a large and typical genus of bivalve molluscs (Lamellibranchs). The thick, ribbed, heart-shaped, equal-valved shell, and the large knee-bent 'foot' are characteristics well known to every one. The shell is closed by two muscles; the hinge has large teeth; there are two minute respiratory siphons. About two hundred living species are known, and have a very wide distribution, though most abundant in the tropical seas. They live freely and gregariously, generally buried in the mud or sand. The foot is used for burrowing, but by it the cockle can also jump a few inches. C. edule is very largely eaten, and is often sold in great quantities on the streets of British towns. The fossil forms are very numerous, and increase from the Silurian onwards. (For figure and structure, see BIVALVES.)