planarian

Nonparasitic flatworm. Planarians are usually small, flat, soft creatures, common both in fresh water and in the sea, where they may be found under rocks and stones in pools. Some of them are brilliantly coloured. They feed on insects, small molluscs, and worms.

The mouth is on the underside of the body, the digestive system varies from a simple bulblike pharynx to a many-branched intestine. The skin is covered with protective vibrating cilia (‘hairs’). Planarians multiply sexually and also by division.

Classification Planarians form the class Turbellaria, which, with Monogenea, Digenea, and Cestoda, comprise the phylum Platyhelminthes.