flatworm vs tapeworm

flatworm and tapeworm both are nouns.

Word	Noun	Adjective	Verb	Adverb
flatworm	Yes	No	No	No
tapeworm	Yes	No	No	No

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

flatworm: parasitic or free-living worms having a flattened body
tapeworm: ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates

Other hyponyms of flatworm include planaria, planarian, fluke, trematode, trematode worm, cestode.

flatworm (noun)	tapeworm (noun)
parasitic or free-living worms having a flattened body	ribbonlike flatworms that are parasitic in the intestines of humans and other vertebrates