polychaete vs segmented worm

polychaete and segmented worm both are nouns.

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

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

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

Other hypernyms of polychaete include annelid, annelid worm.

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