Any of various small, chiefly freshwater flatworms of the order Tricladida, having a soft, broad, ciliated body, a three-branched digestive cavity, and the ability to regenerate body parts.
[From New Latin Plānāria, genus name, from feminine of Late Latin plānārius, on level ground, from plānus, flat; see pelə-2 in the Appendix of Indo-European roots.]
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