How does a jellyfish live without a brain?

Question from Tomas Pirozzi

Clusters of nerve cells help to coordinate the running of an animal’s body, but they consume energy and are costly to make and maintain. Because of this, some animals have evolved to get by without them.

Jellyfish have nets of nerves that allow them to detect chemicals, vibrations and light. These trigger built-in reflexes that enable them to move, eat and reproduce. They essentially live on autopilot. Incredibly, sponges have taken it one step further, doing away
with nerves altogether.

Answered by Laura Mears for Brain Dump in How It Works issue 115.

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