Starfish pump seawater through their veins instead of blood.

While starfish have plenty of limbs, they’re sorely lacking in other biological departments. For instance, these unique sea creatures don’t have a brain — or even blood. Instead, starfish are able to move, breathe, and feed thanks to the life-sustaining seawater coursing through their veins.

Starfish possess what’s called a “water vascular system,” which is also present in other echinoderms such as sea urchins and sea cucumbers. This system is composed of a series of water-filled canals, and as seawater passes through the canals, it delivers nutrients and oxygen to the starfish. The water vascular system also aids in locomotion: As sacs within the system contract, they push fluid into the starfish’s feet, allowing those limbs to elongate and grab onto their surroundings.