Picture of Contact with Sea Urchin
Contact with Sea urchin. Sea urchins don't attack, but if you step on one or somehow get impaled by their spines, it can be painful and potentially dangerous. Try to remove the spines as soon as possible to minimize the reaction as well as any possible secondary infection from the wound. The tips of the sea urchin spines have tiny claw-like pincers called pedicellariae which carry venom. Symptoms vary depending on the species. Reactions can range from pain, redness and swelling to (rarely) an extreme allergic reaction, trouble breathing and even death.
Text Source: MedicineNet / Merck Manuals