Any member of the class Gastropoda, the largest group of the phylum Mollusca, consisting of about 65,000 species. Gastropod, which means “belly-footed,” refers to the broad tapered foot on which these animals glide. The class comprises the snails, which have a shell into which the animal can withdraw, and the slugs—snails whose shells have been reduced to an internal fragment or completely lost in the course of evolution. Gastropods are among the few groups of animals to have successfully radiated in the ocean, fresh waters, and on land. Because of the challenges presented by these diverse habitats, gastropods are very difficult to characterize. A few are used as food, a very few transmit animal diseases (only a fraction of these have been found to carry the agents of human and animal disease), and the shells of some are used as ornaments or in making jewelry. The main role of gastropods is as scavengers, feeding on dead plant or animal matter, or as predators.
Source: Encyclopaedia Britannica 2002