littleneck clam vs round clam

littleneck clam and round clam both are nouns.

Word	Noun	Adjective	Verb	Adverb
littleneck clam	Yes	No	No	No
round clam	Yes	No	No	No

As nouns, round clam is a hypernym of littleneck clam; that is, round clam is a word with a broader meaning than littleneck clam:

littleneck clam: a young quahog
round clam: an edible American clam; the heavy shells were used as money by some American Indians

Other hypernyms of littleneck clam include hard-shell clam, hard clam, Mercenaria mercenaria, quahaug, quahog, Venus mercenaria.

As nouns, round clam is a hypernym of littleneck clam; that is, round clam is a word with a broader meaning than littleneck clam:

littleneck clam: a quahog when young and small; usually eaten raw; an important food popular in New York
round clam: Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes

Other hypernyms of littleneck clam include hard-shell clam, quahaug, quahog.

littleneck clam (noun)	round clam (noun)
a young quahog	an edible American clam; the heavy shells were used as money by some American Indians
a quahog when young and small; usually eaten raw; an important food popular in New York	Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes