class Hexapoda vs order Siphonaptera

class Hexapoda and order Siphonaptera both are nouns.

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

class Hexapoda (noun)	order Siphonaptera (noun)
insects; about five-sixths of all known animal species	fleas