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Nematoda Digestive System

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Animals of the phylum Nematoda are also known as roundworms. In this lesson you'll learn about the digestive system of nematodes and what makes them unique.

Phylum Nematoda

The phylum Nematoda is a fascinating group of animals. Known as roundworms, nematodes range from very small to over 20 feet long! Some are parasitic, like the heartworms that infest dogs and cats, others are agricultural pests that attack plant roots, while others are helpful decomposers that clean up soil and other parts of ecosystems.

It's estimated that there are as many as 500,000 different species of nematodes, and they are found in just about every environment you can imagine! As weird as they can seem, their digestive system has some similarities to ours. Let's go into more detail.

Some nematodes are very long, while others are microscopic.
nematode

The Complete Digestive System

Nematodes have what is called a complete digestive system. This means that at one end is a mouth, and on the other end is an anus. Unlike some animals (like the starfish) where intake and output occur in the same place, a complete digestive tract is one where food travels one way only.

The evolutionary advantages of having a complete digestive tract are numerous. For example, this type of digestion is more efficient because each section of the digestive tract is specialized to perform a specific function.

Components

The digestive system of a nematode is made up of three main parts: the stomodeum, the intestine, and the proctodeum.

  1. The stomodeum is the beginning of the digestive tract where we find the mouth opening, esophagus (also called the pharynx), and the buccal cavity (the area inside the mouth). Here, food is churned up and mixed with enzymes in preparation for the rest of the digestive process.
  2. On the other end of the worm is the proctodeum, which is where waste is expelled after the food is processed and moved through the digestive tract. By this point, nutrients and other goodies have been absorbed from the food in other areas of the digestive system.
  3. In between these two openings, and much like in our own digestive system, we find the intestine. It is much simpler than ours though, just a tube-like structure running the length of the animal. There is no stomach or other components like we find along our digestive system either. In the intestine, enzymes are produced that aid in digestion and help absorb nutrients. But unlike our intestines, there are no muscles in a nematode's intestine to move food through it. Instead, it's the movement of the worm itself that helps food travel along from one end to the other.

Stylet and Cuticle

In addition to these main digestive system components, some other structures that may be present. Carnivorous nematodes may have teeth or something called a stylet, a piercing, tube-like mouthpart which is sharp and can be driven into prey items. In some nematodes this structure is not used for jabbing but is instead hollow and used for sucking out liquids from prey items. Some nematodes even have lips, up to six different ones!

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