Cockles live on the bed of the Wadden Sea. Probably the most common mussels in the Wadden Sea, they are heart-shaped when viewed from the side and have rugged, ribbed shells.
They burrow into the mud using a tongue-like foot by pressing the foot into the sand, anchoring it, and then pulling the shell under. The bigger cockles can be easily recognised in small puddles on the tidal flats by the sunlight reflecting off their two siphon openings. The siphon is a short breathing tube through which the cockle takes in seawater; it uses its gills to filter plankton from the water.