Cockles are burrowing shellfish which live in the firm
sand in sheltered bays. They are easy to recognise by their rather fat shells, marked with strong ribs. In suitable places they live in enormous numbers, perhaps as one million to the acre, and their shells can be found in heaps on the tideline.
They are among the most commonest shells on Dublin Bay. Living cockles bury themselves below the surface of the sand where the tide covers it every day. They can be found easily by digging down a few inches. The cockle holds its shell tightly closed when it is dug out, but will become active again soon after it is put back in the water. A few minutes after a cockle is placed in a pool on the sand, it opens its shell a little and puts out a white, fleshy foot. It moves around and then uses the foot to scoop away the sand and the shell gradually sinks in to the hole. In a minute or two, it disappears completely below the surface. The foot has a tough skin, but is quite soft inside. When the cockle pumps blood into the foot, it grows much larger. A cockle is also a very common shell in Ireland.
