Flatworms are simple, soft-bodied invertebrates belonging to the phylum Platyhelminthes. They have a flattened body shape, which allows them to absorb nutrients and oxygen directly through their skin. Flatworms can be found in various environments, including freshwater, saltwater, and moist terrestrial habitats. There are three main classes of flatworms: Turbellaria (free-living flatworms), Trematoda (parasitic flukes), and Cestoda (tapeworms). Some flatworms are known for their remarkable regenerative abilities, allowing them to regrow lost body parts. They play important roles in ecosystems, serving as both predators and prey.