amphibian vs amphibia

amphibian and amphibia both are nouns.

Word	Noun	Adjective	Verb	Adverb
amphibian	Yes	Yes	No	No
amphibia	Yes	No	No	No

amphibian (noun)	amphibia (noun)
cold-blooded vertebrate typically living on land but breeding in water; aquatic larvae undergo metamorphosis into adult form	the class of vertebrates that live on land but breed in water, frogs, toads, newts, salamanders, caecilians
an airplane designed to take off and land on water
a flat-bottomed motor vehicle that can travel on land or water

amphibian (adjective)	amphibia (adjective)
relating to or characteristic of animals of the class Amphibia