pla·​nar·​ia plə-ˈner-ē-ə How to pronounce planaria (audio)
plural planaria also planarias
: any of a genus (Planaria) of 2-eyed planarian worms
broadly : planarian

Examples of planaria in a Sentence

Recent Examples on the Web In their natural state planaria prefer the smooth and sheltered to the rough and open. Rowan Jacobsen, Scientific American, 21 Sep. 2020 Somehow, despite the total loss of their brains, those planaria had retained the memory of the liver reward. Rowan Jacobsen, Scientific American, 21 Sep. 2020 To find out whether voltage changes really altered the ways that cells passed information to one another, Levin turned to his planaria farm. Rowan Jacobsen, Scientific American, 21 Sep. 2020 At a school biology club meeting, Polyak cut up flatworms called planaria and watched their heads and tails regenerate. Adithi Ramakrishnan, Dallas News, 17 May 2023 Though often no bigger than an apple seed, planaria are the envy of the animal kingdom. Elizabeth Pennisi, Science | AAAS, 14 June 2018 One hundred and twenty-four of the genes missing from planaria are essential to humans and mice, but the worms seem to do fine without them. John Timmer, Ars Technica, 25 Jan. 2018 More distantly related worms called planaria can be cut into multiple pieces and see each piece regrow an entirely new body. John Timmer, Ars Technica, 25 Jan. 2018 Plenty of other animals can do this — from planaria to newts. David Freeman /, NBC News, 28 Jan. 2018

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'planaria.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


New Latin, from feminine of Late Latin planarius lying on a plane, from Latin planum plane

First Known Use

1855, in the meaning defined above

Time Traveler
The first known use of planaria was in 1855

Dictionary Entries Near planaria

Cite this Entry

“Planaria.” Dictionary, Merriam-Webster, Accessed 30 May. 2024.

Kids Definition


pla·​nar·​ia plə-ˈnar-ē-ə How to pronounce planaria (audio)
: planarian
especially : any of a common freshwater genus

Medical Definition


pla·​nar·​ia plə-ˈnar-ē-ə, -ˈner- How to pronounce planaria (audio)
capitalized : the type genus of the family Planariidae comprising planarian worms having two eyes
: any worm of the genus Planaria
broadly : planarian
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