Banded diadem urchin

Scientific name : Diadema savignyi

Rounded, not very large test (6 cm diameter), spines long to 20 cm. Variable colour, spines with a typical banding. Anal sac with concentric rings around the anus.
Common in bay and lagoon, on sandy bottoms, sometimes common where the back reef is damaged. Social, it form denses aggregations.
Diadema setosum has non banded spines. Echinothrix calamaris has often banded spines, but larger and open ended.

Associated organisms
The shrimps Saron marmoratus and Saron sp. stay in the vicinity for shelter, like many fishes of the families Apogonidae (cardinal fish) and Aeoliscidae (razor fish).