brachyuran vs crustacean

brachyuran and crustacean both are nouns.

Word	Noun	Adjective	Verb	Adverb
brachyuran	Yes	No	No	No
crustacean	Yes	Yes	No	No

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

brachyuran: typical crabs
crustacean: any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton

brachyuran (noun)	crustacean (noun)
typical crabs	any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton

brachyuran (adjective)	crustacean (adjective)
	of or belonging to the class Crustacea