Planaria

noun

1. The typical genus of Planariidæ. P. torva is an example.
2. 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.
3. Plural form of planarium.
4. free-swimming mostly freshwater flatworms; popular in laboratory studies for the ability to regenerate lost parts