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Planaria sp., or cross-eyed worm, is a common freshwater flatworm. It moves by cilia on the ventral dermis, allowing it to glide along on a film of mucus. Some move by undulations of the whole body by the contractions of muscles built into the body wall. Planaria are a member of the class Turbellaria and the phylum of flatworms, Platyhelminthes. They exibit an extraordinary ability to regenerate lost body parts. For example, a Planaria split length wise or crosswise will regenerate into 2 separate individuals. The size ranges from 3 to 12mm, and the body has two eye-spots (also known as ocilli) that can detect the intensity of light. The eye-spots act as photoreceptors and are used to move away from light sources.
Planaria are common to many parts of the world and reside in fresh water ponds.
The most frequently used in the laboratory is the brownish Dugesia tigrina. Other common varieties are the blackish Planaria maculata and Planaria dorotocephalia.
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