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.

Jellyfish

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.

Coral

Coral is known for creating multi-colored and textured reefs as each tiny individual coral dies and leaves its colorful shell behind, attached to its neighbor. But corals are actually fierce little warriors. When a predator looms, or when two beds of coral grow into one another’s territory, the little polyps send out their tentacles to poison and sting the interlopers into submission.

Sea Anemone

Lacking a central nervous system, the anemone has a neural net of sorts which keeps it on the lookout for food. The anemone nabs passers-by with its venomous tentacles, paralyzing and then consuming its prey. After eating, the anemone spews the waste back out the same opening, as its digestive chamber only has one door, functioning as both mouth and anus.

Sea Squirt

Sea squirts are filter feeders that look kind of like inflatable straws. Weirdly, a newborn sea squirt gets to have a brain, but loses its intellect when it grows up. A baby squirt looks like a tadpole and has a teeny brain and one eye, but no way to eat. It swims to the ocean floor where it attaches itself and then grows into an adult, absorbing its now-useless eye, tail and brain in the process.

Portuguese Man-O-War

Sometimes called a “blue bottle” for its translucent sac that floats on the surface, this creature is actually a traveling colony of polyps that stick together to create the Portuguese Man-o-War. The creatures that form the Man-o-War each specialize in one facet of survival, like defense, reproduction or eating. The living Man-o-War parts are born together and stay bonded for life.