The common. For example, their body symmetry. Nematodes

The phylum Nematoda is a diverse and abundant one on Earth. In this lesson, you’ll learn about the type of body symmetry that these roundworms exhibit.

What are Nematodes?

With over 25,000 named species, my guess is you’ve at least come across a nematode once or twice in your life.

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These guys are commonly known as roundworms. Some are free-living animals, but many of them are parasitic, meaning that they live off of other organisms.

Nematodes live in all different environments, and many are parasitic pests.

Nematodes inhabit all different types of environments, too.

Some live in the soil, performing the important function of decomposing dead and decaying material. Others live in freshwater and marine environments. And, as we already discussed, some live within other organisms.

Nematode Body Plans

Although there is great diversity among nematodes, their body plans are actually quite similar. Some exist as very small organisms (only a millimeter or two), while others may be more than 7 meters long! But in general they have some things in common. For example, their body symmetry. Nematodes have what is called bilateral symmetry (‘bi’ means ‘two’).

This means that their bodies can be divided into two halves that are mirror images of each other.This is very much like you and me. If you take a good look at your own body, you will notice that your right and left sides are mirror images of each other as well, and we see this same symmetry in the nematode worms.

Bilaterally symmetric organisms have two halves that are mirror images of each other.
Like the spokes of a wheel, radially symmetric structures are the same on all sides.

radially symmetric

What’s interesting about nematodes, though, is that their heads are not bilaterally symmetrical like ours. Instead, the head is radially symmetrical, meaning that it is the same on all sides.

Think of the spokes of a wheel radiating from the center, or slices of a whole pizza to understand how this symmetry works. Inside this head are various structures, including the pharynx, or throat, at the back of the mouth, sensory organs, and even up to six sets of lips!

Lesson Summary

Nematodes, commonly referred to as roundworms, are both abundant and interesting animals. Inhabiting just about everywhere on Earth (including the bodies of other organisms!), these guys have got it made.There’s more than meets the eye with nematodes too, because despite their simple outward appearance they actually have bilateral symmetry. This means that they have two sides that are identical to each other, just like we do.

But instead of having a head that is also bilaterally symmetric, theirs is radially symmetric. Here we find that instead of two identical halves, each is the same as it radiates outward from a central point.


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