planarian
noun
pla·nar·i·an
plə-ˈner-ē-ən 
: triclad
especially
: any of various dark-colored freshwater triclad flatworms (family Planariidae) with two eyespots and a triangular head
Examples of planarian in a Sentence
Recent Examples on the Web
To find out, the researchers started taking planarian embryos (from the species named Schmidtea polychroa) and slicing them in half.
—
John Timmer, ArsTechnica, 18 Apr. 2025
For those of us whose memory of high school biology hasn't faded entirely, planarians will probably sound very familiar.
—John Timmer, ArsTechnica, 18 Apr. 2025
The new species belongs to a group of flatworms known as planarians, which are typically non-parasitic.
—Irene Wright, Miami Herald, 9 Apr. 2025
This capacity is all too evidently lacking in humans—so how do planarians do it?
—Philip Ball, Scientific American, 18 Apr. 2023
Even a small part of a planarian can regenerate into a full worm with the typical shape and proportions.
—Philip Ball, Scientific American, 18 Apr. 2023
Cut off a planarian's head, and the creature will simply sprout a new one in its place.
—Marla Broadfoot, Discover Magazine, 25 Nov. 2015
So how did the the planarian lose its centrosomes?
—Elizabeth Preston, Discover Magazine, 10 Jan. 2012
If one animal could become an honorary superhero, my vote would be for the planarian.
—Seriously Science, Discover Magazine, 15 July 2013
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John Timmer, ArsTechnica, 18 Apr. 2025
For those of us whose memory of high school biology hasn't faded entirely, planarians will probably sound very familiar.
—John Timmer, ArsTechnica, 18 Apr. 2025
The new species belongs to a group of flatworms known as planarians, which are typically non-parasitic.
—Irene Wright, Miami Herald, 9 Apr. 2025
This capacity is all too evidently lacking in humans—so how do planarians do it?
—Philip Ball, Scientific American, 18 Apr. 2023
Even a small part of a planarian can regenerate into a full worm with the typical shape and proportions.
—Philip Ball, Scientific American, 18 Apr. 2023
Cut off a planarian's head, and the creature will simply sprout a new one in its place.
—Marla Broadfoot, Discover Magazine, 25 Nov. 2015
So how did the the planarian lose its centrosomes?
—Elizabeth Preston, Discover Magazine, 10 Jan. 2012
If one animal could become an honorary superhero, my vote would be for the planarian.
—Seriously Science, Discover Magazine, 15 July 2013
Cite this Entry
“Planarian.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/planarian. Accessed 14 Jul. 2025.
Copy CitationKids Definition
planarian
noun
pla·nar·i·an
plə-ˈnar-ē-ən
-ˈner-
: any of an order of small soft-bodied mostly water-dwelling flatworms having cilia
especially
: one living in fresh water and having two eyespots and a triangular head
Medical Definition
planarian
noun
pla·nar·i·an
-ē-ən
: any of the family Planariidae or order Tricladida comprising small soft-bodied ciliated mostly aquatic turbellarian worms
planarian
adjective
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