pelecypod vs bivalve

pelecypod and bivalve both are nouns.

Word	Noun	Adjective	Verb	Adverb
pelecypod	Yes	Yes	No	No
bivalve	Yes	Yes	No	No

As nouns, pelecypod and bivalve are synonyms defined as:

pelecypod and bivalve: marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together

Other synonyms of pelecypod include lamellibranch.

pelecypod (noun)	bivalve (noun)
marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together	marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together

pelecypod (adjective)	bivalve (adjective)
bivalve	used of mollusks having two shells (as clams etc.)