phylum Arthropoda vs class Hexapoda

phylum Arthropoda and class Hexapoda both are nouns.

Word	Noun	Adjective	Verb	Adverb
phylum Arthropoda	Yes	No	No	No
class Hexapoda	Yes	No	No	No

phylum Arthropoda (noun)	class Hexapoda (noun)
jointed-foot invertebrates: arachnids, crustaceans, insects, millipedes, centipedes	insects; about five-sixths of all known animal species