Source : Webster's Revised Unabridged Dictionary (1913)

Planaria \Pla*na"ri*a\, n.; pl. L. {Planari[ae]}, E. {-rias}.
   [NL. See {Planary}.] (Zo["o]l.)
   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.

Source : WordNet®

planaria
     n : free-swimming mostly freshwater flatworms; popular in
         laboratory studies for the ability to regenerate lost
         parts [syn: {planarian}]