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

Because pets travel substantial distances each year, researchers suggest that this form of movement could meaningfully contribute to the worldwide spread of certain invasive flatworm species.

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

Euhaplorchis californiensis, for one, is a trematode flatworm that, in its larval stage, looks a bit like a sperm, with a big head and long tail.

From Scientific American • May 18, 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