planarian

American

[pluh-nair-ee-uhn] / pləˈnɛər i ən /

noun

Zoology.

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.

planarian British

/ pləˈnɛərɪən /

noun

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

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

planarian Scientific

/ plə-nâr′ē-ən /

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.

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”; see plane ¹, -ary + -an

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

planarian

Adult planarian stem cells can transform into any type of cell, unlike most animals' stem cells, which are carefully restricted to forming only a few cell types.

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

María Lucila Scimone, a researcher at M.I.T.’s Whitehead Institute for Biomedical Research, first noticed these cells while studying Schmidtea mediterranea, a planarian common to bodies of freshwater in Southern Europe and North Africa.

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

These are planarian worms, and though not of prepossessing appearance generally, are extremely interesting animals to study.

From Country Walks of a Naturalist with His Children by W. (William) Houghton

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Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023