MOLLUSCS

PHYLUM: MOLLUSCA

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.

The African land snail can be 30 cm (12 in) long. Like all snails, it carries a coiled shell on its back and withdraws into the shell when threatened. It moves slowly on a large, muscular foot, using slime to ease the way. Its mouth, underneath its head, contains the denticle-covered radula.

The blue-ringed octopus is a mollusc that does not have a shell. It has a large brain and big eyes. It uses its eight arms to crawl, but also squirts water from inside its body to move more quickly.

PHYLUM: MOLLUSCA

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.

Class: Bivalvia

(clams, mussels, oysters, scallops)

Features: shell in two symmetrical halves with hinge

Class: Polyplacophora

(chitons)

Features: shell made up of several overlapping plates

Class: Gastropoda

(snails, slugs)

Features: suction foot, many have spiral shell

Class: Scaphopoda

(tusk shells, razor shells)

Features: long, tubular shells, burrow into sediment

Class: Cephalopoda

(nautiloids, squid, octopus)

Features: tentacles, suckers