sandfish vs percoidean

sandfish and percoidean both are nouns.

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

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

sandfish: either of two small silvery scaleless fishes of the northern Pacific that burrow into sand
percoidean: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of sandfish include percoid, percoid fish.

sandfish (noun)	percoidean (noun)
either of two small silvery scaleless fishes of the northern Pacific that burrow into sand	any of numerous spiny-finned fishes of the order Perciformes
fish of sandy areas of western Pacific and Indian oceans having an angular snout for burrowing into sand