Source : Webster's Revised Unabridged Dictionary (1913)

Mollusca \Mol*lus"ca\, n. pl. [NL. See {Mollusk}.] (Zo["o]l.)
   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.

   Note: Formerly the Brachiopoda, Bryzoa, and Tunicata were
         united with the Lamellibranchiata in an artificial
         group called Acephala, which was also included under
         Mollusca. See {Molluscoudea}.

Source : WordNet®

Mollusca
     n : gastropods; bivalves; cephalopods; chitons [syn: {phylum
         Mollusca}]