Our Privacy/Cookie Policy contains detailed information about the types of cookies & related technology on our site, and some ways to opt out. By using the site, you agree to the uses of cookies and other technology as outlined in our Policy, and to our Terms of Use.


Does a Jellyfish Have a Brain?

i Photos.com/Photos.com/Getty Images

Jellyfish (phylum Cnidaria) aren't only a source of interest because of their grace and impressive predation techniques. They're also intriguing from a biological standpoint because they literally don't have brains -- at least, not ones that are anything like those of human beings. These marine animals are comparatively basic organisms.

No Brains for Jellyfish

These plankton lack brains. They lack nervous systems that can deliver brain signals to different sections of their bodies, too. They accomplish these tasks, however, through the use of basic touch receptors that are situated by their mouths and over their tentacles' foundations. Through neurons, jellyfish can pick up on water chemistry shifts, smells and the motion of prey, enabling them to effectively seize their next meals. These receptors also allow jellyfish to perform their reactions to various external factors. These neuron communities are commonly referred to as "nerve nets."

Balance and Light

Jellyfish nerve nets feature several things that assist the creatures in their routine actions. Statocysts are one such example. These receptors focus on balance. They help jellyfish to determine in which exact direction something is, whether above or below them. Many jellyfish also even possess rhopalia, which are sensory components that can pick up on the emergence of light, for example. When jellyfish can pick up on light, they can differentiate between the murky sea floor and bright water surface. When it comes to handling all of the things they need to do to stay alive, jellyfish depend on their nerves.

Some Jellyfish Have Eyes

Box jellyfish of the class Cubozoa have elaborate eyes -- with actual retinas, corneas and lenses. These jellyfish do indeed react to visuals in their surroundings. Researchers aren't sure how exactly they analyze the things they see, however, due to their lack of brain, according to the Smithsonian Ocean Portal. They may accomplish this through the assistance of their nerve rings.

Jellyfish Body Basics

Jellyfish don't have brains, and that's just where things begin. They don't have many of the body parts that are typical in other animals. They also don't have ears, hearts or bones. They are, however, equipped with muscles. They utilize their muscles for feeding and swimming alike. Water makes up roughly 95 percent of jellyfish bodies. Jellyfish do not have any hard or tough components of their physiques. Since jellyfish are almost entirely water, they tend to be extremely delicate, even when they're particularly big.