Molluscs

Molluscs are a group of animals with soft bodies, and they make up one of the largest phyla of the animal kingdom. To protect their soft bodies most molluscs have shells, like the snail or the oyster. But some, like the octopus, are completely unprotected.

There are more than 80,000 living species of molluscs, and many more fossil yarieties. They are grouped in these six classes:

Monoplacophora have simple, cap-shaped shells. Only three living species are known, though many fossils have been found. The first living specimen, genus Neopilina, was discovered 11,800 feet (3,590 m) down in the Pacific as recently as 1952.

Amphineura are simple sea creatures. Some are worm-like; others, such as the chitons, have shells made up of eight plates.
Gastropoda form the largest group, and include snails, slugs, and limpets.

Scaphopoda, or tusk shells, have long tube-like shells. They burrow in the sand and mud of the sea-bed, usually in deep water.

Pelecypoda or bivalves have shells made in two halves (called 'valves') hinged together. They include clams and oysters.

Cephalopoda is a class including squids, cuttlefishes, and octopuses-and some of the largest sea creatures as far as length goes.

All molluscs have a fairly well developed nervous system, and the octopuses have well developed brains, too. Most molluscs have a single broad-soled foot, on which the animal can crawl by a series of muscle contractions. Molluscs tend to move slowly, but octopuses and squids are fast swimmers. Many molluscs, such as oysters, swim about when they are young, then settle down to a quiet life on the sea floor.