clam: burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness
bivalve: marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together
bacteria: (microbiology) single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; taxonomy is difficult; often considered to be plants