If a spine is damaged in the process, it will be regrown. The purple urchin is not as sedentary as its habit of living in holes might suggest. Many urchins do not live in holes, especially where the rock is too hard. When sand is piled up in their usual habitat, they may move upward. Herbivorous, feeding on fixed algae like sea lettuce.
Sexes are separate.
Both eggs and sperm are shed into the water for chance fertilization. The free-swimming larvae may live planktonic existence for several months, and then metamorphose quickly into young urchins. They are also hosts to a variety of parasites. Communalistic relationships in which the urchins are not harmed also exist. One species of sea urchin is used for protection by two different species of fish.