Planaria (n.)

flat worm-like animal, 1819, from Modern Latin (1776) noun use of fem. of Late Latin planarius, literally "on level ground" (here used to mean "flat"), from Latin planum, planus "flat, level, even, plain" (from PIE root *pele- (2) "flat; to spread"). Related: Planarian.

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Definitions of Planaria from WordNet

planaria (n.)
free-swimming mostly freshwater flatworms; popular in laboratory studies for the ability to regenerate lost parts;
Synonyms: planarian