Crustacea vs crustaceous

Crustacea is a noun but crustaceous is not a noun.

Word	Noun	Adjective	Verb	Adverb
Crustacea	Yes	No	No	No
crustaceous	No	Yes	No	No

Crustacea (noun)	crustaceous (noun)
class of mandibulate arthropods including: lobsters, crabs, shrimps, woodlice, barnacles, decapods, water fleas

Crustacea (adjective)	crustaceous (adjective)
	being or having or resembling a hard crust or shell
	of or belonging to the class Crustacea