They are found in all waters of the world. Because they are not aggressive, contact with humans is accidental or deliberate. Swimmers step on them in shallow surf. Sea urchins have 2 types of venomous organs, spines and pedicelaria.
Spines usually produce puncture wounds.
Pedicelaria are small, delicate seizing organs that release venom. Rarely, a victim may experience fatigue, weakness, muscle aches, shock, paralysis, and respiratory failure. Death may occur. Repeat as necessary to control pain. Use tweezers to remove any spines in the wound.