n. pl. - One of the grand divisions of the animal kingdom,
including the classes Cephalopoda, Gastropoda, PteropodaScaphopoda, and
Lamellibranchiata, or Conchifera. These animals have an unsegmented
bilateral body, with most of the organs and parts paired, but not
repeated longitudinally. Most of them develop a mantle, which incloses
either a branchial or a pulmonary cavity. They are generally more or
less covered and protected by a calcareous shell, which may be
univalve, bivalve, or multivalve.