The Collaborative International Dictionary of English v.0.48:

pelecypod \pelecypod\ n.
   1. A marine or freshwater mollusk having a soft body with
      platelike gills enclosed within two shells hinged
      together; a member of the Pelecypoda.

   Syn: bivalve, lamellibranch.
        [WordNet 1.5] pelecypod

The Collaborative International Dictionary of English v.0.48:

pelecypod \pelecypod\ pelecypodous \pelecypodous\adj.
   1. same as lamellibranchiate.

   Syn: lamellibranch, lamellibranchiate.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

pelecypod
    adj 1: bivalve [syn: lamellibranch, pelecypod,
           pelecypodous]
    n 1: marine or freshwater mollusks having a soft body with
         platelike gills enclosed within two shells hinged together
         [syn: bivalve, pelecypod, lamellibranch]