class Hexapoda vs order Ephemeroptera

class Hexapoda and order Ephemeroptera both are nouns.

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

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