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T he Gastropoda, comprising the snails & slugs, are one of the 7 classes of Phylum Mollusca, which also includes the bivalves and cephalopods. This large and successful invertebrate group has managed to adapt to almost every environment; an estimated 105,000 survive in various forms worldwide. Although the vast majority are scavengers, some act as parasites (the shelless parenteroxenos doglieli - the longest gastropods at up to 130 cm - lives only as a parasite inside sea cucumbers). Some are now predators, and some species, like (such as the familiar helix aspersa ) are raised as food by humans. The gastropods (Latin for "stomach-footed") are classified into 3 subclasses:

Prosobranchs - mostly marine snails, some freshwater and terrestrial species. Fairly primitive forms, many with an operculum.
Opisthobranchs - the sea slugs, some sea snails. Hermaphroditic, with the shell often internalized or lost.
Pulmonates - mostly land snails and slugs, but some freshwater and marine species exist. Hermaphroditic, often with a more advanced and concentrated nervous system.

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Text Copyright © 1998 A Blair. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission is encouraged. Disseminate at will. All images are copyright of their respective owners, see References for sources. Work in progress.

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Last Updated: April 8,1998