Picture of Contact with Sea Urchin
Sea urchins are echinoids that have spines that can be up to several inches long. Stepping on, falling on, or brushing against sea urchins can cause spines to fall off and embed into the skin. The sting is painful and unless the spines are removed, an infection will result. The process is tedious, but every spine out of the dozens that may be embedded must be removed in order to relieve the symptoms and prevent infection.
Text Reference: Merck Manual: “Sea Urchin Stings”