Cockles
In the rockpools around North Wales you will often find limpets, snails and slugs. These are molluscs and are also called Gastropods.
Some slugs have no shells and are very colourful, called 'nudibranchs',
but most have shells and strong teeth to scrape algae off rocks and to eat seaweed. Some tropical Gastropods are very poisonous and feed on fish much bigger than themselves. Their poison is strong enough to kill a human, but the ones in the shores around Great Britain don't do that!
Limpet size and shape grows according to whether they live near crashing waves like at South Stack off the shores of Anglesey or in a more protected area like the tiny coves around Borth y Gest off the Lleyn Peninsula.
Common Whelk (Buccinium undataum)
This is a large whelk at 11cm long, it feeds on tube worms, cockles, other bivalve molluscs and scavenges. They are generally found on muddy sand, gravel and rock and are common on all British coasts. Their empty egg mass is often seen on the seashore.
Empty Shells
Among the shells you may find, with or without owners, are those of BIVALVES. These are molluscs like mussels, cockles and oysters. Bivalves have a hinged shell with strong muscles to keep the two halves together. Some can lock in water to keep them from drying out when the tide goes out e.g. Mussels.
Edible or Blue Mussel (Mytilus edulis)
These have 2 siphons. One sucks in water (and food) and the other spits it out (taking away any unwanted waste). They are called 'filter feeders', Mussels attach themselves to rocks and piers, (check out local piers at Bangor, Llandudno and Beaumaris) using very strong 'byssus threads' They are usually found in large groups, piled on top of each other, depending on space.
Edible Cockle (Cerastoderma edule)
Cockles bury themselves in mud or sand to hide from predators and feed. They are also filter feeders. Younger cockles are eaten by crabs on the lower shore and larger cockles by birds at the top of the shore. Rather like a tree lays down rings of growth, they lay down ridges in their shells for each year of growth.
