Starfish Have No Brain

It seems impossible that an animal could hunt and navigate its world without a central command center, yet sea stars (as they are more accurately known) do just that. Their entire body is run by a decentralized nerve net, an intricate web of nerves that handles local reflexes and sensations. For actions requiring coordination, such as moving in a specific direction, a nerve ring encircling the mouth acts as a switchboard, ensuring all five (or more) arms work in concert. Each arm has a degree of autonomy, but the ring allows one arm to take the lead and guide the others.

This unique nervous system is surprisingly effective. At the tip of each arm, a sea star has a primitive eyespot that can detect light and shadow, helping it move towards food or away from potential threats. This allows it to perform sophisticated tasks, most famously prying open the shells of bivalves like clams and mussels. Using the relentless, coordinated pull of hundreds of tiny tube feet, the sea star can force the shell open just enough to insert its stomach and digest its meal. It’s a remarkable example of how life can evolve complex solutions without following the vertebrate blueprint of a centralized brain.