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.


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


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

Copyright © 2007 Dorling Kindersley


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