Long-spined sea urchin

Diadema savignyi has a usually black, spherical, slightly-flattened test up to about 9 cm (3.5 in) in diameter. The brittle, thin, hollow spines grow in tufts and can be as long as 25 cm (10 in). They are usually black but can also be grey, dark brown or purple. They may be banded with lighter and darker shades in juveniles and the occasional individual sea urchin is completely white. Diadema savignyi is similar in appearance to the closely related Diadema setosum with which it is sympatric, that is, the two species share a common range and frequently come into contact with each other. Diadema savignyi can be distinguished by the fact that it has iridescent green or blue lines in the interambulacral areas and around the periproct, a cone-shaped region surrounding the anus. In a small number of individuals there are pale coloured spots at the aboral (upper) ends of the interambulacrals. Another distinguishing feature is that D. savignyi does not have a thin orange ring round the periproct whereas D. setosum does.