The Nervous System of Platyhelminthes

Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

The nervous system should invoke images of a brain or spinal cord, but what about animals that have neither? What about those flatworms that lack a real brain or spine? Let's look at Platyhelminthes, who have a unique nervous system.

What Are Platyhelminthes?

What in the world is a platyhelminth? How do you even pronounce that name? Well platyhelminth is pronounced, 'plat-ee-hell-min-th.' Platyhelminthes is a phylum in the animal kingdom of taxonomy. The animals in this phylum are also known as flatworms because, as you can tell by the name, they are typically flat.


These organisms would be considered fairly simple by human standards and occur much earlier in the evolutionary history of Earth than humans. There are four classes of flatworms, three of which are parasites and one class,turbellarians that are not. The turbellarians appear to have eyes and a face which is not technically true as these features are not part of simple organisms. The other classes are much scarier looking with fang-looking structures near their mouthparts.

Along with the idea of these being simple organisms, they do have a number of systems to keep them alive such as respiratory, digestive, and (what you came here to learn about) a nervous system. In each of the classes of Platyhelminthes, we see the nervous system concentrated in the anterior region of the animal, most commonly the head of the animal.

Nervous System

When thinking about the nervous system of a flatworm, we need to suspend our ideas of a nervous system. In a human, we can picture the brain connected to the spinal cord that runs dorsally or down our back with smaller nerves running off of that creating this giant complex system of nerve cells all across the body.

In planarians, a type of flatworm or platyhelminth, there exists in the head region, cerebral ganglia. Cerebral ganglia are multiple ganglions which are just clusters of nerve cells. These nerve cells exist in large and numerous clusters in the head of the animal as a sort of primitive brain. For the planarians, the cerebral ganglia control the nervous system of the animal.

In other subgroups of Platyhelminthes, the ganglia are not present, but a bundle of nervous tissue similar to a nerve net is. This nerve net looks similar to an actual 'net', but it is the brain of the animal.

In orange you can see the nervous system. Ganglia located near the head with attached main nerves running lengthwise.
Flatworm nervous system

Attached to either the ganglia or the nerve net (depending on the animal) would be two main nerves running lengthwise through the animal. Branching off of these would be smaller, accessory-type nerves to allow the animal to function. This would be similar to human beings as we have a brain with an attached spinal cord and branching accessory nerves. The differences here would be many, but again, we have one main nerve where the flatworms have two which form a ladder-like appearance with the rungs of the ladder being the accessory nerves.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account