Roundworms
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: February 25, 2015
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C HAPTER
Chapter 1. Roundworms
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Roundworms
• Describe the major features of the roundworms.
• Describe parasitic roundworms.
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.
Roundworms
The word "worm" is not very scientific. This informal term describes animals (usually invertebrates) that have long
bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms (
Figure 1.1). They are classified in the phylum Nematoda, which has over 28,000 known species. Some scientists
believe there could be over a million species of Nematodes.
Nematodes are slender bilaterally symmetrical worms, typically less than 2.5 mm long. The smallest nematodes
are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still,
reaching over a meter in length. The worm body is often covered with ridges, rings, bristles, or other distinctive
structures. The radially symmetrical head of a nematode also has distinct features. The head is covered with sensory
bristles and, in many cases, solid "head-shields" around the mouth region. The mouth has either three or six lips,
which often have a series of teeth on their inner edges.
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FIGURE 1.1
Nematodes can be parasites of plants and animals.
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. This is a significant
difference from the incomplete digestive system of flatworms. The roundworm digestive system also include
a large digestive organ known as the gut. Digestive enzymes that start to break down food are produced here.
There is no stomach, but there is an intestine which produces enzymes that help absorb nutrients. The last
portion of the intestine forms a rectum, which expels waste through the anus.
3. Roundworms also have a simple nervous system with a primitive brain. There are four nerves that run the
length of the body and are connected from the top to the bottom of the body. At the anterior end of the animal
(the head region), the nerves branch from a circular ring which serves as the brain. The head of a nematode
has a few tiny sense organs, including chemoreceptors, which sense chemicals.
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. Most Nematodes are parasitic, with over 16,000 parasitic species described. 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
1.2), is caused by infection with a type of roundworm.
Most parasitic roundworm eggs or larvae are found in the soil and enter the human body when a person picks them
up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly
through the skin. The best solution to these diseases is to try to prevent these diseases rather than treat or cure them.
Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include
• lack of a clean water supply,
• inadequate sanitation measures,
• crowded living conditions, combined with a lack of access to health care and low levels of education.
Summary
• Roundworms have a body cavity with internal organs and a simple nervous system.
• Roundworms can be free-living or parasitic.
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Chapter 1. Roundworms
FIGURE 1.2
One roundworm parasite causes elephantiasis, a disease characterized by
swelling of the limbs.
Explore More
Use the resources below to answer the questions that follow.
Explore More I
• Nematode Movement at http://www.youtube.com/watch?v=SpgjnXEFadg (1:52)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57288
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?
Explore More II
• Mushroom Mycelium Feeding on Nematodes at http://www.youtube.com/watch?v=0n04wCkIpuQ (1:41)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57289
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1. Why do some fungi trap nematodes?
Explore More III
• Heartworm Quiz at http://www.heartwormsociety.org/pet-owner-resources/quiz.html
Review
1. What is a roundworm?
2. How are the internal structures of the roundworms different from flatworms?
3. What is the main cause of many parasitic diseases caused by roundworms?
References
1. Courtesy of the Agricultural Research Service. Nematodes can be parasites of plants and animals . Public
Domain
2. Courtesy of the Centers for Disease Control and Prevention. A swollen leg caused by elephantiasis, resulting
from a roundworm parasite . Public Domain
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