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9.5: Roundworms

Difficulty Level: At Grade Created by: CK-12
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What is heartworm?

You may have heard that you need to protect your pets from heartworm. Heartworms are a type of roundworm. They can be parasites in cats and dogs. That means, once they infect your pet, they can cause harm. However, there are preventative treatments available.


The word "worm" is not very scientific. This informal term describes animals that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms (Figure below). They are classified in the phylum Nematoda.

Features of Roundworms

  1. Unlike the flatworms, the roundworms have a body cavity with internal organs.
  2. A roundworm has a complete digestive system, which includes both a mouth and an anus. They also include a large digestive organ known as the gut.
  3. Roundworms also have a simple nervous system with a primitive brain. The nerves are connected from the top to the bottom of the body.

Nematodes can be parasites of plants and animals

Nematodes can be parasites of plants and animals.

Roundworms in the Environment

Roundworms can be free-living organisms, but they are probably best known for their role as significant plant and animal parasites. Heartworms, which cause serious disease in dogs while living in the heart and blood vessels, are a type of roundworm. Roundworms can also cause disease in humans. Elephantiasis, a disease characterized by the extreme swelling of the limbs (Figure below), is caused by infection with a type of roundworm.

One roundworm parasite causes elephantiasis, a disease characterized by swelling of the limbs.


  • roundworm: Invertebrate animals with a round, elongated body that are often parasites of plants and animals.


  • Roundworms have a body cavity with internal organs and a simple nervous system.
  • Roundworms can be free-living or parasitic.


Use the resources below to answer the questions that follow.

  1. How does the movement of a nematode differ from the movement of an earthworm?
  2. Why can't a nematode move like an earthworm?
  3. What is the purpose of the nematode's cuticle?
  4. How is the growth of a nematode similar to the growth of a crab?
  1. Why do some fungi trap nematodes?
  2. What do fungi use this resource for?


  1. What are some of the roles of roundworms in the environment?
  2. How are the internal structures of the roundworms different from flatworms?

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Invertebrate animals with a round, elongated body that are often parasites of plants and animals.

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Difficulty Level:
At Grade
7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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