Definition of Lamellibranchia
: a class of Mollusca including the clams, oysters, and mussels, having the body bilaterally symmetrical, compressed, and more or less completely enclosed within the mantle that secretes a bivalved shell whose right and left parts are connected by a hinge over the animal's back, having no distinct head, usually two lamelliform gills on each side of the body, and the ventral region differentiated in most of the forms into a muscular plowshare or tongue-shaped foot by means of which the animal burrows or moves about, and having the posterior margins of the mantle lobes drawn out in the burrowing species into tubes through which water passes into and out of the mantle cavity
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