polychaete vs annelid worm

polychaete and annelid worm both are nouns.

Word	Noun	Adjective	Verb	Adverb
polychaete	Yes	No	No	No
annelid worm	Yes	No	No	No

As nouns, annelid worm is a hypernym of polychaete; that is, annelid worm is a word with a broader meaning than polychaete:

polychaete: chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles
annelid worm: worms with cylindrical bodies segmented both internally and externally

Other hypernyms of polychaete include annelid, segmented worm.

polychaete (noun)	annelid worm (noun)
chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles	worms with cylindrical bodies segmented both internally and externally