mussel shrimp vs crustacean

mussel shrimp and crustacean both are nouns.

Word	Noun	Adjective	Verb	Adverb
mussel shrimp	Yes	No	No	No
crustacean	Yes	Yes	No	No

As nouns, crustacean is a hypernym of mussel shrimp; that is, crustacean is a word with a broader meaning than mussel shrimp:

mussel shrimp: tiny marine and freshwater crustaceans with a shrimp-like body enclosed in a bivalve shell
crustacean: any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton

mussel shrimp (noun)	crustacean (noun)
tiny marine and freshwater crustaceans with a shrimp-like body enclosed in a bivalve shell	any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton

mussel shrimp (adjective)	crustacean (adjective)
	of or belonging to the class Crustacea