holocephalian vs holocephalan

holocephalian and holocephalan both are nouns.

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

As nouns, holocephalian and holocephalan are synonyms defined as:

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

holocephalian (noun)	holocephalan (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