What Are Nematodes? - Definition, Properties & Examples

What Are Nematodes? - Definition, Properties & Examples
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  • 0:01 Worms, Worms Everywhere!
  • 1:10 Parasitic Nematodes
  • 2:21 Beneficial Nematodes
  • 3:00 Lesson Summary
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Lesson Transcript
Instructor: Gretchen Baumle
Nematodes are roundworms that are found in every environment on Earth. While some species are harmful parasites, others play a vital role in nutrient cycling and medical research.

Worms, Worms Everywhere!

Nematodes are more commonly called roundworms and can be found in aquatic habitats, soil, snowy tundras and hot deserts, inside plants and animals, and just about every place in between. Just a handful of rich dirt can have several thousand of these tiny worms!

Nematodes can be very small, at a millimeter or less, or can reach lengths of up to three feet. Their bodies don't have an internal skeleton like human bodies do; instead they have a cuticle, an exoskeleton that doesn't grow with the worm and so is periodically cast off in a shedding process called molting. Nematodes have muscles that run the length of their bodies that, when contracted, produce a thrashing-like movement that propels them forward.

Most species of roundworm have both males and females and reproduce sexually. A female nematode can produce more than 100,000 fertilized eggs in a single day! They all have a complete digestive system, which means that they have two openings: a mouth and an anus. Like most other animals we're familiar with, nematodes exhibit bilateral symmetry, meaning they have identical right and left halves.

Parasitic Nematodes

Many roundworm species are parasites that survive in or on another living organism, called the host, and often cause harm to it while doing so. About 60 species to date are known to be parasites of humans. These include pinworms, which lay their eggs around the anus and are often parasites of children because their eggs are passed in fecal matter. And, well, we all know how dirty kids can be!

Hookworms are another human parasite. They can penetrate the skin (especially the bottom of the feet when walking barefoot in contaminated soil) and travel up to the lungs. Once in the lungs, the worms have high hopes of being coughed up and swallowed down into the digestive system, where they can feed off our nutrients for years!

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