Apr 30, 2025
You might think having a brain is necessary to survive, but nature says otherwise. Some creatures go on to live full lives hunting, moving, and reacting to their surroundings without a central brain. Here are 10 surprising animals that live without a brain.
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Jellyfish have no brain, heart, or bones instead just a simple nerve net that helps them sense the world and react accordingly. Despite their squishy look, they've survived for over 500 million years and can still hunt, swim, and even glow in the dark.
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Starfish or sea stars have no brain, but they do have a decentralized nerve ring and sensory cells in each arm. That allows them to move, find food, and even regenerate lost limbs, all without any central processing center.
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Sea urchins may look like living pin-cushions, but they operate just fine without a brain. A nerve ring and light-sensitive cells across their body help them detect danger, find algae to eat, and move their spines in defense.
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Sponges are among the simplest animals alive. With no brain, organs, or nervous system, they rely on water currents to feed and clean themselves. Yet they’ve been around for over 600 million years with a low-maintenance survival.
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Sea cucumbers look like squishy tubes, and that’s pretty much what they are. No brain, just a basic nervous system. Still, they manage to crawl across the ocean floor, clean up debris, and even shoot their own guts at predators.
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Corals may look like colourful plants, but they’re actually animals that are actually brainless. They form colonies, feed through tentacles, and build massive reef systems that support entire ecosystems.
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Clams don’t have a brain just paired ganglia or nerve clusters, to help them react to stimuli. They can open, close, and even dig into the sand to escape danger. It’s all because of the muscle memory and quick reflexes.
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These brainless creatures use stinging tentacles to paralyze prey and bring it to their mouths. They might not be fast, but they’re deadly, and their simple nerve net helps them react to touch and movement.
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Tiny freshwater animals, hydras, have no brain but use a basic nerve net to contract and feed. They're also known for their near-immortality; in fact some hydras don’t seem to age at all.
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Planarians don’t technically have a brain, just a cluster of nerve cells called a ganglion. Yet they can learn simple tasks, respond to light, and regrow if cut in half, including rebuilding that ganglion from scratch.
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