bivalve: Class of mollusks that use their foot to attach themselves to rocks or to burrow into mud, i.e. clams. cephalopod: Class of mollusks characterized by a set of arms or tentacles; i.e. octopus.
A bivalve is a type of mollusk that burrows into the mud or attaches itself to rocks with its foot. A cephalopod is a mollusk with arms or tentacles, such as an octopus.
