The word "Mollusca" comes from the Latin molluscus, or soft.

Including such diverse animals as snails, oysters and octopuses, this is one of the most familiar of all the large animal groups.

Characteristics (1) Calcareous shell with underlining mantle of tissue; (2) ventral, muscular foot; (3) gut with two openings; (4) body cavity.

Size Less than an inch to 55 feet in the giant squid.

Habitat All waters and land.

	Class Monoplacophora -- Neopilina (3 species) -- Living members of this class, thought extinct for 300 million years, were first collected in 1952 from a deep ocean trench at 11,778 feet. Subsequent finds indicate their distribution may be worldwide in deep seas. Most species are a scant inch long, with a single cap-shaped shell and a broad, flat foot.	Class Amphineura -- chitons (about 600 species) -- With a large flat sucker-foot and heavy mantle margin, chitons cling to rocky shores, particularly in the Pacific Northwest, scraping up algae. One to 12 inches long, they are protected by a shell of eight overlapping pictures.
	Class Gastropoda -- snails (about 100,000 species) -- This is the largest class of mollusks. Marine species include snails, conches and sea slugs. Fresh-water snails have both gillbearing and airbreathing species; the 19,000 species of land snails have a cavity beneath the mantle adapted as a lung. A broad, flat foot, a distinct head with tentacles and a spirally twisted shell are generally typical of this class.	Class Bivalvia -- bivalves (about 30,000 species) -- Including the clams, oysters and scallops, the bivalves have a laterally flatenned body enclosed within two hinged shells. Most are marine, though some are found in fresh water.
	Class Scaphopoda -- tusk shells (about 200 species) -- The one- to two-inch tusk shells burrow head first in the sea bottom. The tapered end of the shell projects above the sand surface, and water for respiration is pumped into and out of its opening. Scaphopods feed on small organisms caught by many little tentacles on the head.	Class Cephalopoda -- octopus, squid, nautilus (about 1,000 species) -- Eight or more suction-cupped tentacles enable cephalopods to seize prey. A water jet from a funnel propels them. Nautilus alone has an external shell. Most of the class are under two feet in length, but the Atlantic giant squid reaches 55 feet.

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This page was last updated on 06/01/2010.