pearlfish vs percoidean

pearlfish and percoidean both are nouns.

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

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

pearlfish: found living within the alimentary canals of e.g. sea cucumbers or between the shells of pearl oysters in or near shallow seagrass beds
percoidean: any of numerous spiny-finned fishes of the order Perciformes

Other hypernyms of pearlfish include percoid, percoid fish.

pearlfish (noun)	percoidean (noun)
found living within the alimentary canals of e.g. sea cucumbers or between the shells of pearl oysters in or near shallow seagrass beds	any of numerous spiny-finned fishes of the order Perciformes