Banded Sea Urchin

Echinothrix calamaris

The banded sea urchin (Echinothrix calamaris), also called the double-spined urchin, is a distinctive sea urchin found throughout the Indo-Pacific. Adults reach a test diameter of about 5-10 cm with two distinct types of spines: short, fine, venomous spines that are banded in yellow-brown to dark colors and can deliver a painful sting, and longer, thicker primary spines that are typically banded in light and dark colors or may be uniformly colored. They inhabit coral reef crevices, under ledges, and in rocky holes at depths of 1-70 meters, emerging at night to graze on algae and organic material. Their dual-spine defense system provides both physical and chemical protection against predators. The venomous secondary spines can penetrate wetsuits and skin, causing intense pain. Despite the hazard, their dramatic appearance with the contrasting banded spines makes them interesting subjects for careful observation and photography on tropical reef dives.