Everyone needs a brain to live, right? Not necessarily! Some of our fellow animals have no such thing, yet manage to survive just fine. Instead of having a brain, some animals have clusters of nerve cells called ganglia to help direct traffic in their bodies. But amazingly, most of the animals on this list don’t even have ganglia to help them out. When it comes to doing what they need to do to survive, these animals don’t give it a second thought. In fact, they don’t even give it a first thought.

Sea Star

Even though they don’t have a brain or even ganglia, sea stars do have some sense of touch, sight and smell. Each of the sea star’s arms can sense the world around it. When one of the arms smells something good to eat, it cuts off power to the other arms and starts pulling the entire creature towards the food source.

Sea Cucumber

Sea cucumbers don’t have grey matter, but they have ingenious defense mechanisms. When under attack, sea cucumbers can startle (and gross out) their attacker by suddenly disgorging their guts and internal organs. Or they can opt to eject long sticky tubes from their anus to ensnare and possibly disable the predator – permanently.


As you can literally see, jellyfish don’t have much for internal organs. Instead of a brain, jellies have what’s known as a neural net — a system of nerve cells interwoven all over the animal’s body. Jellyfish survive this way whether they’re 1 mm wide or 100 feet long.

Sea Sponge

Not only are they brainless, but sponges don’t even have digestive, nervous or circulatory systems. Instead, they have a bunch of unassigned cells that can go around their body turning into whatever kind of cell is needed at the time. And even without any internal organs, sponges can sneeze! When they detect an irritation, a sponge will “inhale” water and then contract its body and “sneeze” out the irritant. Spongey sneezes can last up to 60 minutes!

Sea Lily

These creatures look more like underwater ferns, but they are actually animals. Sea lilies are rooted to the ocean floor and gather food via their feathery arms, which apparently requires no thinking at all. They look delicate, but sea lilies are tough enough to endure the pressure of living up to 20,000 feet below the surface.

Sea Urchin

Urchins creep around the ocean floor looking for food, but they have to make it up as they go; there is no planning ahead for a creature lacking in brains. They need not worry about self-defense either, thanks to the sharp spines covering their bodies.

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