planarian

American  

[pluh-nair-ee-uhn] / pləˈnɛər i ən /

noun

Zoology.

1. any of various free-swimming, mostly freshwater flatworms of the class Turbellaria, having an undulating or sluglike motion: popular in laboratory studies for the ability to regenerate lost parts.

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planarian British  

/ pləˈnɛərɪən /

noun

1. any free-living turbellarian flatworm of the mostly aquatic suborder Tricladida, having a three-branched intestine

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planarian Scientific  

/ plə-nâr′ē-ən /

1. Any of various small, chiefly freshwater flatworms of the class Turbellaria, having soft, broad, ciliated bodies shaped like a leaf. Planarians have a mouth on their lower side that is often closer to the tail than the head, and a three-branched digestive cavity. If a planarian is cut into several pieces, each piece can grow into a whole new organism.

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Etymology

Origin of planarian

1885–60; < New Latin Planari ( a ) a flatworm genus (noun use of feminine of Late Latin plānārius level, on level ground; taken to mean “flat”; plane ¹, -ary + -an

Example Sentences

"The big discovery is a property of the whole planarian permitting both subtle local interactions and global signaling events that allow stem cells to achieve these remarkable feats of regeneration," said Benham-Pyle.

From Science Daily • Oct. 29, 2025

Cut a chunk out of a planarian, and it will regrow exactly those tissues that were removed, neither more nor less.

From Scientific American • May 31, 2023

The research suggests that cellular guides hidden throughout the planarian body may make it possible for the worm’s newly grown neurons to retrace their steps.

From New York Times • Jun. 29, 2020

Gurley, K. A., Rink, J. C. & Sánchez Alvarado, A. β-catenin defines head versus tail identity during planarian regeneration and homeostasis.

From Nature • Nov. 21, 2017

It is now nearly forty years since the presence of chlorophyl in certain species of planarian worms was recognized by Schultze.

From Scientific American Supplement, No. 324, March 18, 1882 by Various