polychaete vs lugworm

polychaete and lugworm both are nouns.

Word	Noun	Adjective	Verb	Adverb
polychaete	Yes	No	No	No
lugworm	Yes	No	No	No

As nouns, lugworm is a hyponym of polychaete; that is, lugworm is a word with a more specific, narrower meaning than polychaete:

polychaete: chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles
lugworm: marine worms having a row of tufted gills along each side of the back; often used for fishing bait

Other hyponyms of polychaete include lobworm, lug, sea mouse, bloodworm.

polychaete (noun)	lugworm (noun)
chiefly marine annelids possessing both sexes and having paired appendages (parapodia) bearing bristles	marine worms having a row of tufted gills along each side of the back; often used for fishing bait