Molluscs

Snails, mussels, and squid are all different types of mollusc. Many molluscs have shells made of calcium carbonate. They may have outer shells, as snails do, or internal shells, held in inside their bodies, like those of cuttlefish.

The main groups of mollusc are the gastropods (snails), bivalves (cockles and mussels), and the cephalopods (squid, octopus, nautiloids and the extinct groups ammonites and belemnites).