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.