Diadema Sea Urchin

As a member of the class Echinoidea, the anatomy of Diadema setosum is that of a typical sea urchin. All of the animal's internal organs are enclosed within the near-spherical, black test that is essentially the body and skeleton of the organism. However, the body is not perfectly spherical – Diadema tests are slightly dorso-ventrally compressed. Protruding outwards from the central body are the long spines iconic of a sea urchin's appearance. Like the other members of the family Diadematidae, the spines of D. setosum are extremely long and narrow in proportion to its body. The spines, often black but sometimes brown-banded, are hollow and contain a mild venom. D. setosum can be distinguished from other species in the genus Diadema by the presence of five white spots on the animal's test, strategically located between the urchin's ambulacral grooves.

Diadema setosum is a widely distributed species of sea urchin. Its range stretches throughout the Indo-Pacific basin including Malaysia, longitudinally from the Red Sea and then eastward to the Australian coast. Latitudinally, the species can be found as far north as Japan and its range extends as far south as the southern tip of the African east coast.