Sea urchin
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Diadema (genus)
It is one of the most abundant, widespread, and ecologically important shallow water genera of tropical sea urchins. It is found in all tropical oceans, although is ubiquitous in the Indo-Pacific region, where it inhabits depths down to 70 m. However each species inhabits roughly separate areas of ocean.
Speciation within the genus can be difficult to confirm, partly due to hybridisation, which is at least known to occur between "Diadema savignyi" and "Diadema setosum".