gempylid vs percoidean

gempylid and percoidean both are nouns.

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

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

gempylid: snake mackerels; elongated marine fishes with oily flesh; resembles mackerels; found worldwide
percoidean: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of gempylid include percoid, percoid fish.

gempylid (noun)	percoidean (noun)
snake mackerels; elongated marine fishes with oily flesh; resembles mackerels; found worldwide	any of numerous spiny-finned fishes of the order Perciformes