ostracod vs crustacean

ostracod and crustacean both are nouns.

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

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

ostracod: 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

ostracod (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

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