scaphopod vs shellfish

scaphopod and shellfish both are nouns.

Word	Noun	Adjective	Verb	Adverb
scaphopod	Yes	No	No	No
shellfish	Yes	No	No	No

As nouns, shellfish is a hypernym of scaphopod; that is, shellfish is a word with a broader meaning than scaphopod:

scaphopod: burrowing marine mollusk
shellfish: invertebrate having a soft unsegmented body usually enclosed in a shell

Other hypernyms of scaphopod include mollusc, mollusk.

scaphopod (noun)	shellfish (noun)
burrowing marine mollusk	invertebrate having a soft unsegmented body usually enclosed in a shell
	meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)