The purple-spined sea urchin, Arbacia punctulata, can be found in shallow water from Massachusetts to Cuba. It is related to sea stars, sand dollars and sea cucumbers—the star pattern can sometimes be seen from above!
Each moveable spine is attached with a ball and socket joint and is used for protection as well as locomotion. The surface of an urchin's shell has rows of tiny tube feet, which allow the animal to stay grasped onto rocks against the tug of the waves and grab bits of shells or seaweed for camouflage.
The urchin’s spines can sense light! Urchins have generalized light sensitivity all over their bodies.
Along with humans, wolffish and gulls are predators of sea urchins.
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