Placodermi vs class Placodermi

Placodermi and class Placodermi both are nouns.

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

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

Placodermi and class Placodermi: extinct group of bony-plated fishes with primitive jaws

Placodermi (noun)	class Placodermi (noun)
extinct group of bony-plated fishes with primitive jaws	extinct group of bony-plated fishes with primitive jaws