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
Example Sentences
Recent Examples on the Web But upon decapitation, the frontmost part of the remaining planarian can assume the duties of the now-missing head. 
Ed Yong, The Atlantic, 8 Oct. 2021 The biologist Thomas Hunt Morgan once estimated that a full planarian could regenerate from just one 279th of its body. Ed Yong, The Atlantic, 8 Oct. 2021 After two weeks, a complete and healthy animal—a planarian of Theseus—crawled away. Ed Yong, The Atlantic, 8 Oct. 2021 The most astonishing part was that Levin hadn’t touched the planarian’s genome. Matthew Hutson, The New Yorker, 3 May 2021 Severance occurs when the tail tip adheres to the substratum and the rest of the planarian pulls away. Chris Ciaccia, Fox News, 23 May 2018 For the planarian, the researchers were able to identify roughly 1,000 likely genes that are probably specific to these organisms. John Timmer, Ars Technica, 25 Jan. 2018 That's exactly what happened with earlier attempts to sequence the planarian and axolotl genomes. John Timmer, Ars Technica, 25 Jan. 2018 Reader Terri Shofner then alerted us to Ho's video of the odd-looking creature, which experts say is likely an unknown species of the genus Bipalium, known by the common names hammerhead worm and broadhead planarian. Liz Langley, National Geographic, 15 July 2017 See More
Ed Yong, The Atlantic, 8 Oct. 2021 The biologist Thomas Hunt Morgan once estimated that a full planarian could regenerate from just one 279th of its body. Ed Yong, The Atlantic, 8 Oct. 2021 After two weeks, a complete and healthy animal—a planarian of Theseus—crawled away. Ed Yong, The Atlantic, 8 Oct. 2021 The most astonishing part was that Levin hadn’t touched the planarian’s genome. Matthew Hutson, The New Yorker, 3 May 2021 Severance occurs when the tail tip adheres to the substratum and the rest of the planarian pulls away. Chris Ciaccia, Fox News, 23 May 2018 For the planarian, the researchers were able to identify roughly 1,000 likely genes that are probably specific to these organisms. John Timmer, Ars Technica, 25 Jan. 2018 That's exactly what happened with earlier attempts to sequence the planarian and axolotl genomes. John Timmer, Ars Technica, 25 Jan. 2018 Reader Terri Shofner then alerted us to Ho's video of the odd-looking creature, which experts say is likely an unknown species of the genus Bipalium, known by the common names hammerhead worm and broadhead planarian. Liz Langley, National Geographic, 15 July 2017 See More Word History
Etymology
New Latin Planaria
First Known Use
1854, in the meaning defined above
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