limpet vs shellfish

limpet and shellfish both are nouns.

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

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

limpet: mollusk with a low conical shell
shellfish: meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)

limpet (noun)	shellfish (noun)
any of various usually marine gastropods with low conical shells; found clinging to rocks in littoral areas	invertebrate having a soft unsegmented body usually enclosed in a shell
mollusk with a low conical shell	meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)