We pets, or maybe starfish, jellyfish and

We are going to get an understanding of the type of symmetry nematodes display. This lesson is also going to talk about how nematodes produce movement.


What are some of the different animals that you have heard of? Surely dogs and cats that you have as pets, or maybe starfish, jellyfish and whales that you like to see at aquariums. Perhaps you thought of different species of birds like bluebirds or eagles.I am almost certain that one particular category of animals did not come to mind just now. It is highly unlikely that you named any nematodes. Nematodes are very tiny roundworms that are often parasitic in nature, meaning that they live off of other living organisms. Types of nematodes include hookworms, C.

elegans, and pinworms.There are estimated to be over 22,000 species of nematodes. Some are free living, others cause diseases and some are even studied by scientists in order to understand how our bodies work and disease processes. Let’s focus on nematode symmetry and how they produce movement.

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Nematodes are tiny roundworms that can only bend side to side.

Picture of nematode movement

Nematode Symmetry

Now, take a moment and look at yourself in the mirror. Do you see any way to divide yourself into two equal parts? Of course you do. It is immediately obvious that you could draw a line down the center of your body between your eyes, through your nose and down to your belly button. The fact that you can draw a line lengthwise to be divided into two equal halves that are mirror images of each other means that you have bilateral symmetry.

A butterfly is an example of bilateral symmetry, which means it can be divided in equal halves that are mirror images.

Diagram of butterfly showing bilateral symmetry

Nematodes also display bilateral symmetry. A straight line can be drawn starting from the head of the nematode, between the eyes and continued down the length of the nematode to the tail. The structures on one side of the line are mirror images to the structures on the opposite side of the line.One interesting thing about worms that are classified as nematodes, is that their heads display radial symmetry even though the entire worm is bilaterally symmetrical.

The head being radially symmetrical means that any line drawn through the center of the head, will produce mirror images. This differs from bilateral symmetry in which only one line drawn lengthwise produces mirror images.

Nematode Movement

So, exactly how do these tiny roundworms move? They move using muscles, just like we move using muscles. That’s about where the physical similarities end between us and nematodes.

The muscles inside nematodes are arranged so that they stretch the length of the body, and are under the control of two nerves. One nerve is on the ventral or belly side and the other is on the dorsal or back of the nematode.The nerves send electrical signals that cause the muscles to contract and relax.

This muscle action bends the worm from side to side, and the bending propels the worm forward. Nematodes are not capable of crawling, or even sliding like a snake, because all of their muscles are parallel with the body. The movement looks a lot more like the worm is wiggling around rather than moving in a straight line.

Lesson Summary

Nematodes are tiny roundworms that may be parasitic. Nematodes have bilateral symmetry, which means there is a line lengthwise that can divide them into two equal halves that are mirror images. The heads of nematodes have radial symmetry which means that any line drawn through the center produces mirror images. Nematodes move using lengthwise muscles that bend the worm side-to-side to propel it forward.

Movement is controlled by a nerve on the underside and another nerve on the back.


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