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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.
(Animals) any free-living turbellarian flatworm of the mostly aquatic suborder Tricladida, having a three-branched intestine
[C19: from New Latin Plānāria type genus, from Late Latin plānārius level, flat; see plane1]
pla•nar•i•an(pləˈnɛər i ən)
any of various free-swimming, mostly freshwater flatworms, having an undulating or sluglike motion.