holocephalan vs holocephalian

holocephalan and holocephalian both are nouns.

Word	Noun	Adjective	Verb	Adverb
holocephalan	Yes	No	No	No
holocephalian	Yes	No	No	No

As nouns, holocephalan and holocephalian are synonyms defined as:

holocephalan and holocephalian: fish with high compressed head and a body tapering off into a long tail

holocephalan (noun)	holocephalian (noun)
fish with high compressed head and a body tapering off into a long tail	fish with high compressed head and a body tapering off into a long tail