n.
or platyhelminth
Any of a phylum (Platyhelminthes) of soft-bodied, usually much-flattened worms , including both free-living and parasitic species.
Flatworms live in a variety of marine, freshwater, and terrestrial habitats worldwide. They range in length from much less than an inch (a fraction of a millimeter) to 50 ft (15 m) and are of three main types: turbellarians (including the planarian ), trematodes (see fluke ), and cestodes (see tapeworm ). Flatworms are bilaterally symmetrical and lack respiratory, skeletal, and circulatory systems and a body cavity. Turbellarians are mostly free-swimming, but trematodes and cestodes are parasites.