scaphopod vs tusk shell

scaphopod and tusk shell both are nouns.

Word	Noun	Adjective	Verb	Adverb
scaphopod	Yes	No	No	No
tusk shell	Yes	No	No	No

As nouns, tusk shell is a hyponym of scaphopod; that is, tusk shell is a word with a more specific, narrower meaning than scaphopod:

scaphopod: burrowing marine mollusk
tusk shell: any of various seashore mollusks having a tapering tubular shell open at each end and a foot pointed like a spade for burrowing

Other hyponyms of scaphopod include tooth shell.

scaphopod (noun)	tusk shell (noun)
burrowing marine mollusk	any of various seashore mollusks having a tapering tubular shell open at each end and a foot pointed like a spade for burrowing