No Blood, No Brains—but Hundreds of Feet Starfish are unusual creatures. First of all, they’re not even fish. They’re echinoderms (like sea urchins and sand dollars), so marine biologists prefer to call them sea stars instead. They also don’t have any blood. They pump filtered seawater through a vascular system, which allows them to move the hundreds of tiny, water-powered tube feet that cover the underside of their five (or more!) arms. Starfish are predators that can use their arms to pry open clams and mollusks. They eject their stomach through their centrally located mouths to begin digesting their prey, then retract it when finished. Starfish have no brain. To hunt or evade enemies, somehow their decentralized nervous system is able to sense and
respond to their surroundings. Their major organs are in their arms. There’s an eyespot on each tip that is sensitive to light and dark, and their retractable feet are used to move, sense and touch the world around them. Speaking of arms, starfish have incredible regenerative abilities. If they lose an arm (some starfish have up to 40), they can regrow it, usually over the course of a year. In fact, a few species are able to regrow an entire starfish from a single arm! Pictured: mottled star (Evasterias troschelii) Photo by James Capo Text by James Capo and Jeremy Lallier
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