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The Class Gastropoda includes snails and slugs. Most gastropods have a single, usually spirally coiled shell, but the shell is lost or reduced in some groups. Many snails have an operculum, a plate that closes the gastropod's opening. Shelled gastropods have mantles, while those without shells have reduced to absent mantles.
Gastropods have a muscular foot used for creeping in most species. In some, the foot is modified for swimming or burrowing. Most gastropods have a well-developed head that includes eyes at the end of one to two pairs of tentacles.
Gastropods are found worldwide. Gastropods are by far the largest group of molluscs. Their 40,000 species comprise over 80% of living molluscs.
Gastropods are found in freshwater systems, oceans, and on land wherever there is sufficient moisture.
Gastropods lay eggs. The eggs of some species contain a large yolk. Development of the eggs may be within the body, or the eggs may be expelled to develop externally. Eggs develop into larvae. Those species that will develop a shell start it while larvae. As the animal develops, it adds another curl of shell, ending in an opening from which the head and foot of the animal emerge.
Gastropods are sexual, and some forms are hermaphroditic, meaning that a single individual can produce both egg and sperm. These individuals will exchange sperm with another individual rather than fertilizing themselves.
Gastropods feed on very small things. Most of them scrape or brush particles from surfaces of rocks, seaweeds, animals that don't move, and other objects. For feeding, gastropods use a radula, a hard plate that has teeth.
Gastropod feeding habits are extremely varied, although most species make use of a radula in some aspect of their feeding behavior. Some graze, some browse, some feed on plankton, some are scavengers or detritivores, some are active carnivores.