Diadema Urchin, Echinothrix diadema
The Diadema Urchin (Echinothrix diadema), is a species of long spined sea urchin found in the Indo-Pacific oceanic region. It prefers dark reef. It is active at night, and hides in crevices or under rocks during the day.
This urchin grows to a diameter of about 3.15 inches and is generally black in color and always dark. The spines are banded and closed at the tip. The anal sac is spotted light and dark.
This urchin often hosts the shrimp species Stegopontonia commensalis. Another shrimp species, Saron marmoratus, stays close for protection. Species of cardinal fish and razor fish also utilize the Diadema Urchin for protection.
Image Caption: Diadema Urchin, Echinothrix diadema. Wikipedia(CC BY-SA 1.0)