blennioid fish vs percoidean

blennioid fish and percoidean both are nouns.

Word	Noun	Adjective	Verb	Adverb
blennioid fish	Yes	No	No	No
percoidean	Yes	No	No	No

As nouns, percoidean is a hypernym of blennioid fish; that is, percoidean is a word with a broader meaning than blennioid fish:

blennioid fish: elongated mostly scaleless marine fishes with large pectoral fins and reduced pelvic fins
percoidean: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of blennioid fish include percoid, percoid fish.

blennioid fish (noun)	percoidean (noun)
elongated mostly scaleless marine fishes with large pectoral fins and reduced pelvic fins	any of numerous spiny-finned fishes of the order Perciformes