flatworm

American  

[flat-wurm] / ˈflætˌwɜrm /

noun

1. any worm of the phylum Platyhelminthes, having bilateral symmetry and a soft, solid, usually flattened body, including the planarians, tapeworms, and trematodes; platyhelminth.

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flatworm British  

/ ˈflætˌwɜːm /

noun

1. any parasitic or free-living invertebrate of the phylum Platyhelminthes , including planarians, flukes, and tapeworms, having a flattened body with no circulatory system and only one opening to the intestine

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flatworm Scientific  

/ flăt′wûrm′ /

1. Any of various parasitic and nonparasitic worms of the phylum Platyhelminthes, characteristically having a soft, flat, bilaterally symmetrical body. Flatworms lack a coelom (body cavity), respiratory system, and circulatory system, but are the most primitive invertebrates to have a brain. The evolutionary history of flatworms is uncertain, but they share some basic characteristics with rotifers, nematodes, and a few other invertebrate phyla. Cestodes (tapeworms), planarians, and trematodes (flukes) are flatworms.

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Etymology

Origin of flatworm

First recorded in 1895–1900; flat ¹ + worm

Compare meaning

How does flatworm compare to similar and commonly confused words? Explore the most common comparisons:

• flatworm vs. roundworm

Example Sentences

Out of the roughly ten flatworm species that have invaded France, only one was linked to this type of transport: Caenoplana variegata.

From Science Daily • Feb. 14, 2026

A parasite called Heterobilharzia americana, a flatworm commonly referred to as liver fluke, was behind the illness of the 11 dogs.

From Los Angeles Times • Mar. 14, 2024

California killifish infected with a trematode flatworm, for example, are 10 times to 30 times more likely to become meals for birds than uninfected fish.

From New York Times • Jan. 9, 2023

If the flatworm had a cylindrical body, then the cells in the center would not be able to get oxygen.

From Textbooks • Jun. 9, 2022

No, then we’d have to recognize, say, a chimpanzee as being one-one-hundredth sapient, and a flatworm as being sapient to the order of one-billionth.

From Little Fuzzy by Piper, H. Beam