Organisms belonging to the phylum ________ are also called 'flatworms'.

Platyhelminthes

The correct answer is Option (1)- Platyhelminthes

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