The common cockle (Ceratoid duple) shown above is found just below the
surface at low tide.
When covered by water it extends two papillae siphons
just above the surface of the sand or mud and filter feeds by ciliary action.
Much of the material taken in is fine sand, so before cooking cockles must be
kept in clean sea water so that the fine sand particles are ejected by the
The Royal cloak shell, Gloria alliums is above. It is in the Pectin family, and is found in the Indo-Pacific region.
The Prickly cockle, also known as the Spiny cockle, above, is found in European and West African waters in mud and sand down to 350 metres deep. It has thorns or teeth running down the20 or so ribs of the shell, and can grow as big as 115 mm across. It is fairly common. The outside of the shell is usually pale brown, while the inside is white. Predators of this cockle include starfish.
The Heart cockle is found in the Indo-Pacific, and as its name suggests the shell is heart-shaped when viewed from above. It lives among sand and coral debris in a hollow it excavates. It grows to around 4 - 6 cm across. The shell is very thin, so much so that light can penetrate through the shell allowing green algae to live and photosynthesise inside the shell. The Heart cockle has a symbiotic relationship with the algae and it benefits from the metabolites the algae produces, while the algae can grow in an environment safe from grazing.