class Polychaeta vs Polychaeta

class Polychaeta and Polychaeta both are nouns.

Word	Noun	Adjective	Verb	Adverb
class Polychaeta	Yes	No	No	No
Polychaeta	Yes	No	No	No

As nouns, class Polychaeta and Polychaeta are synonyms defined as:

class Polychaeta (noun)	Polychaeta (noun)
marine annelid worms	marine annelid worms