sand eel vs acanthopterygian

sand eel and acanthopterygian both are nouns.

Word	Noun	Adjective	Verb	Adverb
sand eel	Yes	No	No	No
acanthopterygian	Yes	No	No	No

As nouns, acanthopterygian is a hypernym of sand eel; that is, acanthopterygian is a word with a broader meaning than sand eel:

sand eel: very small silvery eellike schooling fishes that burrow into sandy beaches
acanthopterygian: a teleost fish with fins that are supported by sharp inflexible rays

Other hypernyms of sand eel include spiny-finned fish.

sand eel (noun)	acanthopterygian (noun)
very small silvery eellike schooling fishes that burrow into sandy beaches	a teleost fish with fins that are supported by sharp inflexible rays