bivalve
1. any marine or freshwater mollusc of the class Pelecypoda (formerly Bivalvia or Lamellibranchia), having a laterally compressed body, a shell consisting of two hinged valves, and gills for respiration. The group includes clams, cockles, oysters, and mussels
2. of, relating to, or belonging to the Pelecypoda
3. Biology having or consisting of two valves or similar parts
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
bivalve
[′bī‚valv] (invertebrate zoology)
The common name for a number of diverse, bilaterally symmetrical animals, including mollusks, ostracod crustaceans, and brachiopods, having a soft body enclosed in a calcareous two-part shell.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.