pelecypod vs clam

pelecypod and clam both are nouns.

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

As nouns, clam is a hyponym of pelecypod; that is, clam is a word with a more specific, narrower meaning than pelecypod:

pelecypod: marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together
clam: burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness

Other hyponyms of pelecypod include cockle, oyster, ark shell, blood clam, mussel, escallop, scallop, scollop, piddock.

pelecypod (noun)	clam (noun)
marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together	burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness
	flesh of either hard-shell or soft-shell clams
	a piece of paper money worth one dollar

pelecypod (adjective)	clam (adjective)
bivalve

pelecypod (verb)	clam (verb)
	gather clams, by digging in the sand by the ocean