How Many Brains do Jellyfish Have?

Jellyfish have no brains, blood or bones — in fact, the average jellyfish is composed of 94-98% water. A jellyfish consists mostly of a bell-shaped body with tentacles and a mouth.

More facts about jellyfish:

• A group of jellyfish is called either a bloom of jellyfish or a swarm of jellyfish.


• Most jellyfish are carnivorous, feeding off of fish, fish eggs, plankton and smaller jellyfish. Although they do not have a stomach, jellyfish have a gastrovascular cavity that absorbs nutrients.


• In many Asian cultures, jellyfish is served pickled, salted or dried. A processed jellyfish loses more than 90% of its weight in the processing.

Frequently Asked Questions

Do jellyfish have a brain?

No, jellyfish do not have a brain. Instead, they possess a simple nervous system called a "nerve net," which allows them to sense changes in their environment and respond to stimuli without the need for a centralized brain. This nerve net is spread throughout their body, giving them the ability to navigate their watery world.

How do jellyfish function without a brain?

Jellyfish function through their nerve net, which controls their movements and feeding responses. They also have specialized structures called rhopalia, which house sensory organs and help them maintain balance and orientation. Despite lacking a brain, jellyfish are quite adept at surviving and thriving in their marine habitats.

Can jellyfish feel pain?

Since jellyfish do not have a brain or central nervous system, it is believed that they do not experience pain in the way humans or other animals with complex nervous systems do. Their reactions to stimuli are reflexive rather than a response to pain as we understand it.

What kind of sensory capabilities do jellyfish have?

Jellyfish have a range of sensory capabilities despite their lack of a brain. They can detect light, smell chemicals in the water, and respond to touch. Some species have rudimentary eyespots that can sense the direction of light, aiding them in navigating their environments.

How do jellyfish reproduce without a brain?

Jellyfish reproduce both sexually and asexually. In sexual reproduction, males release sperm into the water, which then fertilizes the eggs produced by females. Some jellyfish species can also reproduce asexually by budding, where a part of the jellyfish's body breaks off and develops into a new individual. These processes are controlled by their simple nervous systems.

What is the lifespan of a jellyfish?

The lifespan of a jellyfish varies widely among different species. Some may live for only a few hours after reaching adulthood, while others, like the immortal jellyfish (Turritopsis dohrnii), have the ability to revert back to their juvenile polyp stage, potentially giving them the capacity to live indefinitely under the right conditions.