Also called lamellibranch. Zoology. any mollusk, as the oyster, clam, scallop, or mussel, of the class Bivalvia, having two shells hinged together, a soft body, and lamellate gills.
Botany. having two valves, as a seedcase.
Zoology. having two shells, usually united by a hinge.
having two similar parts hinged together.

1670–80; bi-1 + valve

bivalvular [bahy-val-vyuh-ler] , adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
bivalve (ˈbaɪˌvælv)
1.  pelecypod, Also: lamellibranch 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.  pelecypod, Also: lamellibranch of, relating to, or belonging to the Pelecypoda
3.  biology Also: bivalvate having or consisting of two valves or similar parts: a bivalve seed capsule

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

1660s in reference to mollusks with double shells; 1670s (adj.) in reference to shutters or doors; from bi- + valve. The noun is 1680s in the mollusk sense.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
bivalve   (bī'vālv')  Pronunciation Key 
Any of various mollusks of the class Bivalvia, having a shell consisting of two halves hinged together. Clams, oysters, scallops, and mussels are bivalves. The class Bivalvia is also called Pelecypoda, and was formerly called Lamellibranchia. Compare univalve.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
The lowly bivalve, it seems, has come out of its shell.
Ostracods are small, bivalve crustaceans that can inhabit underwater caves.
The oceanic surf clam pictured below is a bivalve clam.
Bivalve shellfish aquaculture has local and short term impacts in estuaries where it is conducted.
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