pelecypod vs blood clam

pelecypod and blood clam both are nouns.

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

As nouns, blood clam is a hyponym of pelecypod; that is, blood 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
blood clam: red-blooded clam

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

pelecypod (noun)	blood clam (noun)
marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged together	red-blooded clam

pelecypod (adjective)	blood clam (adjective)
bivalve