A worm of a phylum which includes the planarians together with the parasitic flukes and tapeworms. they are distinguished by having a simple flattened body which lacks blood vessels, and a digestive tract which, if present, has a single opening.
Usage examples:
Planarians are free-living flatworms, and have a much simpler life history.
noun
A creature with a flat body that can live inside the bodies of people and animals and often causes disease