Sea Urchins

The basic sea urchin structure recognized by most people consists of a slightly squashed ball covered by a dense bristling of spines. These spines can be thick and blunt, designed mainly for wedging the animal into place on the reef, as those of the Eucidaris metularia at right. Some hard and sharp spines such as those of the urchin below also seem to function primarily for stabilization, although they may also help keep the urchin from being eaten. What predator would want to eat a ball of spines? (Although in fact, some triggerfish and wrasses seem to have no problems with the spines.)