They have a bright yellow-green and brown skeletal covering and are widely distributed in tropical and subtropical waters.
Divers often mistake fire coral for seaweed, and accidental contact is very common.
In addition, they have a sharp, calcified external skeleton that can scrape the skin. Immediate burning or stinging pain develops over 5-30 minutes. Then a red rash with raised wheals or vesicles appears, and itching develops. Lymph gland swelling may occur over time. Rarely, nausea and vomiting has been reported.