How do jellyfish respond to stimuli in their environment if they don’t have a brain and central nervous system?

Even though jellyfish lack a central nervous system (CNS), that doesn’t mean they completely lack neural tissue.

Jellyfish, and many other cnidarians, have what is known as a neural net. Imagine instead of a centralized brain, the “brain” of the jellyfish is spread throughout its entire body. Even in an animal as “simple” as a jellyfish, there are different types neurons with various specializations.

Jellyfish are able to come in contact with something in their environment, and use their sensory receptors to “feel” the physical contact, and use their motor neurons to move, just like many other animals.

In fact, scientists who actually study jellyfish have demonstrated that the jellyfish’s nervous system is more than just a neural net, and there are certain ganglia diffused throughout the entire body where information can be processed.

 Reference: Kathryn Elle