1. A parasitic or free-living worm with a flattened body, belonging to the phylum Platyhelminthes.
Usage: biology; zoology

Examples

• The flatworm is one of the simplest animals with a nervous system.
• Some flatworms are parasites that infect humans and other animals.
• Planaria, a type of flatworm, can regenerate lost body parts.
• Marine biologists studied the flatworm species found in the coral reef.
• The flatworm's body is typically thin and ribbon-like in appearance.