lugworm vs polychaete worm

lugworm and polychaete worm both are nouns.

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

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

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

Other hypernyms of lugworm include polychaete, polychete, polychete worm.

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