DK Science: Molluscs
Slugs, snails, oysters, clams, squid, octopuses, and cuttlefish are very different to look at, but they are all molluscs. They have a ribbon-like tongue, called the radula, covered in thousands of denticles (tiny teeth). Many have a calcium-carbonate shell. Most molluscs live in water, but slugs and snails live on land.
Molluscs have unsegmented bodies generally protected by a shell. There are more than 50,000 species in seven classes, including the following five common ones.
(clams, mussels, oysters, scallops)
Features: shell in two symmetrical halves with hinge