 The name " bivalve " is derived from the Latin bis , meaning " two " , and <unk> , meaning " leaves of a door " . Not all animals with shells with two hinged parts are classified under Bivalvia ; other animals with paired valves include certain gastropods ( small sea snails in the family <unk> ) , members of the phylum Brachiopoda and the minute crustaceans known as ostracods and <unk> . 
