ecrevisse vs shellfish

ecrevisse and shellfish both are nouns.

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

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

ecrevisse: tiny lobster-like crustaceans usually boiled briefly
shellfish: meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)

ecrevisse (noun)	shellfish (noun)
small crayfish of Europe and Asia and western North America	invertebrate having a soft unsegmented body usually enclosed in a shell
tiny lobster-like crustaceans usually boiled briefly	meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)