Sea stars may look slow and simple, but beneath their arms is a hidden world of remarkable engineering. Each sea star has hundreds of tiny tube feet lining the grooves on the underside of its arms. These flexible, suction-tipped structures help the sea star walk, cling to rocks in pounding surf, and even open tightly closed mussel shells.
Tube feet operate using a unique hydraulic system called the hydrovascular system. When water moves through internal canals, the sea star can extend or retract each tube foot like a miniature piston. This allows incredibly precise movements — even though the sea star has no brain in the way we think of it.
At the tip of each arm, sea stars have a tiny eyespot (an ocellus) that detects light, shapes, and large objects. Their tube feet themselves aren’t eyes, but they work together with the eyespot to help the animal navigate.
Sea star eyespots can:
– See light vs. dark
– Sense large shapes like rocks, coral heads, or open water
– Help the sea star orient toward reef structure, which it prefers
– Work collectively (five arms = five “eyes”) for a panoramic sense of surroundings
They cannot:
– See fine detail
– Form sharp images
– Recognize other animals visually
Their vision is roughly equivalent to seeing blurry silhouettes.
During our school tidepool programs, students are often amazed to see how tube feet “march” in coordinated waves. This gentle motion not only moves the sea star forward but also helps it sense its surroundings as each tube foot detects textures and chemical cues in the water.
Request a Teaching Tidepools® school visit