free-swimming mostly freshwater flatworms; popular in laboratory studies for the ability to regenerate lost parts

Small free-living þatworms (Phylum Platyhelminthes) with bilateral symmetry and cephalization. The freshwater type is often used as an experimental organism.

Any species of turbellarian worms belonging to Planaria, and many allied genera. The body is usually flat, thin, and smooth. Some species, in warm countries, are terrestrial.