mollusc vs shellfish

mollusc and shellfish both are nouns.

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

As nouns, mollusc and shellfish are synonyms defined as:

mollusc and shellfish: invertebrate having a soft unsegmented body usually enclosed in a shell

Other synonyms of mollusc include mollusk.

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