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The class Gastropoda or gastropods (also previously known as univalves and sometimes also spelled Gasteropoda) form a major part of the phylum Mollusca. Gastropods are more commonly known as snails and slugs, and include those that live in the sea, in freshwater and on land. This class of animals is second only to the insects in its number of known species. Its fossil history goes back to the Late Cambrian.

Gastropoda is the most highly diversified class in the phylum Mollusca, with 60,000 to 80,000 living snail and slug species. The anatomy, behavior, feeding and reproductive adaptations of gastropods vary very significantly from one clade or group to another, therefore it is very difficult or impossible to make more than a very few general statements about these topics that will be valid for all of the gastropods.

There are 409 recent families of gastropods. Fossil gastropods represent another 202 families. The gastropods include many thousands of species of marine snails and sea slugs, as well as freshwater snails and freshwater limpets, and the terrestrial (land) snails and slugs.

Gastropod Morphology

Gastropod Morphology - WWC Archives

The class Gastropoda has an extraordinary diversification of habitats. Representatives live in gardens, in woodland, in deserts, and on mountains; in small ditches, great rivers and lakes; in estuaries, mudflats, the rocky intertidal, the sandy subtidal, in the abyssal depths of the oceans including the hydrothermal vents, and numerous other ecological niches, including parasitic ones.

Although the name "snail" can be, and often is, applied to all the members of this class, very commonly this word is restricted to those species which have an external shell large enough that the soft parts can withdraw completely into it. Those gastropods without a shell, and those which have only a very reduced or internal shell, are usually known as slugs.

The marine shelled species of gastropod include edible species such as abalone, conches, periwinkles, whelks, and numerous other sea snails which have coiled seashells. There are also a number of families of species such as all the various limpets, where the shell is coiled only in the larval stage, and is a simple conical structure after that.

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