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The generally accepted systematic name (in contrary to some others) of all mussels, clams and scallops-Bivalvia-the two-valve molluscs-refers to the most important character of all bivalves, that separates them from all other molluscs: The shell is separated into two pieces. bivalve's foot is adapted to how it lives and moves. So there are different types of feet in bivalves, from beam-shaped, tongue-shaped or worm-shaped feet. Swimming mussels, as well as completely sessile mussels, often have a largely reduced foot.
  Bivalves are unique among the mollusks for lacking a radula; they feed by siphoning and filtering large particles from water. Some bivalves are epifaunal: that is, they attach themselves to surfaces in the water, by means of a byssus or organic cementation.Others are infaunal: they bury themselves in sand or other sediments. These forms typically have a strong digging foot.or this reason, land snails will drown if left in a bucket of water that they cannot escape from. Aquatic snails do not have the thick slime that land snails have and will quickly dry out,(if they do not suffocate first) when left out of the water.