round clam vs Mercenaria mercenaria

round clam and Mercenaria mercenaria both are nouns.

Word	Noun	Adjective	Verb	Adverb
round clam	Yes	No	No	No
Mercenaria mercenaria	Yes	No	No	No

As nouns, round clam and Mercenaria mercenaria are synonyms defined as:

round clam and Mercenaria mercenaria: an edible American clam; the heavy shells were used as money by some American Indians

Other synonyms of round clam include hard-shell clam, hard clam, quahaug, quahog, Venus mercenaria.

round clam (noun)	Mercenaria mercenaria (noun)
an edible American clam; the heavy shells were used as money by some American Indians	an edible American clam; the heavy shells were used as money by some American Indians
Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes