sea mouse vs polychete worm

sea mouse and polychete worm both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea mouse	Yes	No	No	No
polychete worm	Yes	No	No	No

As nouns, polychete worm is a hypernym of sea mouse; that is, polychete worm is a word with a broader meaning than sea mouse:

sea mouse: any of several large worms having a broad flattened body with a mat of coarse hairs covering the back
polychete worm: chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles

Other hypernyms of sea mouse include polychaete, polychaete worm, polychete.

sea mouse (noun)	polychete worm (noun)
any of several large worms having a broad flattened body with a mat of coarse hairs covering the back	chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles