I have never heard of anyone being hurt by one in a reef tank. But Im sure someone has.
"Like most aquatic life injuries, sea urchin injuries are the result of the animal trying to defend itself. A sea urchin’s spines are its first line of defense. The length and sharpness of an urchin’s spines vary from species to species. Some species have stubby, blunt spines, while other species have long, sharp, venom-filled spines. Razor-sharp spines can easily pierce even a thick wetsuit and lodge deep in a diver’s skin.
Many urchin species, such as the purple sea urchin, have an additional defense mechanism called the pedicellarines. The pedicellarines are tiny, jaw-like structures that can clasp onto a diver’s skin and inject a painful poison. They are nestled down between the urchin’s spines and are difficult for a diver to contact unless he has already impaled himself on the urchin’s spines.
In extreme cases, such as when a diver suffers numerous puncture wounds, the relatively small amount of venom from spines and pedicellarines can accumulate in sufficient quantities to cause severe muscle spasms, faintness, difficulty breathing, and death."
Kinda like half the modern drugs.
