flat·​worm ˈflat-ˌwərm How to pronounce flatworm (audio)
: any of a phylum (Platyhelminthes) of soft-bodied usually much flattened acoelomate worms (such as the planarians, flukes, and tapeworms)

called also platyhelminth

Examples of flatworm in a Sentence

Recent Examples on the Web Consider Levin’s experiments with planaria, the humble flatworm. Sigal Samuel, Vox, 4 June 2024 Maybe in the Cretaceous period flatworms created lines of ecological connection between organisms as different as clams and dinosaurs. Kristi Curry Rogers, Scientific American, 1 Feb. 2024 Severing a flatworm usually just results in two identical flatworms, but something appears to have gone awry in one individual, who returned with another head where his tail should have been. Nathaniel Scharping, Discover Magazine, 13 June 2017 More emojis of plants, mollusks, flatworms, fungi and microorganisms could help spark new conversations about conservation and biodiversity, a new study argues. Corinne Purtill, Los Angeles Times, 12 Dec. 2023 This giant invasive flatworm, a Diversibipalium 'blue,' made its way to a French territory off Africa. Lauren Sigfusson, Discover Magazine, 22 May 2018 Planarian and the Stem Cell Method Take the flatworm, for example, also known as Planarian and one of the most impressive examples of regeneration in the animal kingdom. Sofia Quaglia, Discover Magazine, 6 Feb. 2023 That’s because another predator has moved in: New Guinea flatworms. Sarah Kuta, Smithsonian Magazine, 2 May 2023 This flatworm has truly astonishing powers of regeneration. Seriously Science, Discover Magazine, 15 July 2013

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

Word History

First Known Use

1874, in the meaning defined above

Time Traveler
The first known use of flatworm was in 1874

Dictionary Entries Near flatworm

Cite this Entry

“Flatworm.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/flatworm. Accessed 23 Jun. 2024.

Kids Definition


flat·​worm -ˌwərm How to pronounce flatworm (audio)
: any of a phylum of simple worms (as planarians, flukes, or tapeworms) that have a soft flat body, lack a body cavity, and have bilateral symmetry

Medical Definition


flat·​worm ˈflat-ˌwərm How to pronounce flatworm (audio)
: any worm of the phylum Platyhelminthes : platyhelminth
especially : turbellarian

More from Merriam-Webster on flatworm

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