elasmobranch vs selachian

elasmobranch and selachian both are nouns.

Word	Noun	Adjective	Verb	Adverb
elasmobranch	Yes	No	No	No
selachian	Yes	No	No	No

As nouns, elasmobranch and selachian are synonyms defined as:

elasmobranch and selachian: any of numerous fishes of the class Chondrichthyes characterized by a cartilaginous skeleton and placoid scales: sharks, rays, skates

elasmobranch (noun)	selachian (noun)
any of numerous fishes of the class Chondrichthyes characterized by a cartilaginous skeleton and placoid scales: sharks, rays, skates	any of numerous fishes of the class Chondrichthyes characterized by a cartilaginous skeleton and placoid scales: sharks, rays, skates