flatworm vs trematode

flatworm and trematode both are nouns.

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

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

flatworm: parasitic or free-living worms having a flattened body
trematode: parasitic flatworms having external suckers for attaching to a host

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

flatworm (noun)	trematode (noun)
parasitic or free-living worms having a flattened body	parasitic flatworms having external suckers for attaching to a host