class Gastropoda vs subclass Opisthobranchia

class Gastropoda and subclass Opisthobranchia both are nouns.

Word	Noun	Adjective	Verb	Adverb
class Gastropoda	Yes	No	No	No
subclass Opisthobranchia	Yes	No	No	No

class Gastropoda (noun)	subclass Opisthobranchia (noun)
snails and slugs and their relatives	gastropods having the gills when present posterior to the heart and having no operculum: includes sea slugs, sea butterflies, sea hares