pollyfish vs percoidean

pollyfish and percoidean both are nouns.

Word	Noun	Adjective	Verb	Adverb
pollyfish	Yes	No	No	No
percoidean	Yes	No	No	No

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

pollyfish: gaudy tropical fishes with parrotlike beaks formed by fusion of teeth
percoidean: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of pollyfish include percoid, percoid fish.

pollyfish (noun)	percoidean (noun)
gaudy tropical fishes with parrotlike beaks formed by fusion of teeth	any of numerous spiny-finned fishes of the order Perciformes