amphibia vs class Amphibia

amphibia and class Amphibia both are nouns.

Word	Noun	Adjective	Verb	Adverb
amphibia	Yes	No	No	No
class Amphibia	Yes	No	No	No

As nouns, amphibia and class Amphibia are synonyms defined as:

amphibia and class Amphibia: the class of vertebrates that live on land but breed in water, frogs, toads, newts, salamanders, caecilians

amphibia (noun)	class Amphibia (noun)
the class of vertebrates that live on land but breed in water, frogs, toads, newts, salamanders, caecilians	the class of vertebrates that live on land but breed in water, frogs, toads, newts, salamanders, caecilians