Phylum Platyhelminthes have dorso-ventrally flattened body, hence are called flatworms (Figure). These are mostly endoparasites found in animals including human beings. Flatworms are bilaterally symmetrical. triploblastic and acoelomate animals with organ level of organization. Hooks and suckers are present in the parasitic forms. Some of them absorb nutrients from the host directly through their body surface. Specialized cells called flame cells help in osmoregulation and excretion. Sexes are not separate.
Fig: (a) Tapeworm, (b) Liver fluke
Fertilization is internal and development is through many larval stages. Some members like Planar ia possess high regeneration capacity.
Examples: Taenia (Tapeworm), Fasciola (Liver fluke).