class Hexapoda vs order Ephemerida

class Hexapoda and order Ephemerida both are nouns.

Word	Noun	Adjective	Verb	Adverb
class Hexapoda	Yes	No	No	No
order Ephemerida	Yes	No	No	No

class Hexapoda (noun)	order Ephemerida (noun)
insects; about five-sixths of all known animal species	the order of mayflies or shadflies (Ephemeroptera, Ephemerida)