polyplacophore vs mollusk

polyplacophore and mollusk both are nouns.

Word	Noun	Adjective	Verb	Adverb
polyplacophore	Yes	No	No	No
mollusk	Yes	No	No	No

As nouns, mollusk is a hypernym of polyplacophore; that is, mollusk is a word with a broader meaning than polyplacophore:

polyplacophore: primitive elongated bilaterally symmetrical marine mollusk having a mantle covered with eight calcareous plates
mollusk: invertebrate having a soft unsegmented body usually enclosed in a shell

Other hypernyms of polyplacophore include mollusc, shellfish.

polyplacophore (noun)	mollusk (noun)
primitive elongated bilaterally symmetrical marine mollusk having a mantle covered with eight calcareous plates	invertebrate having a soft unsegmented body usually enclosed in a shell