Long Spined Sea Urchin (Diadema Savignyi) - Blue Touch Aquatics
Long Spined Sea Urchin (Diadema Savignyi) - Blue Touch Aquatics
Long Spined Sea Urchin (Diadema Savignyi)

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Diadema savignyi is a species of long-spined sea urchin belonging to the family Diadematidae. Common names include long-spined sea urchin, black longspine urchin and the banded diadem. It is native to the east coast of Africa, the Red Sea, the Indian Ocean and western Pacific Ocean.

It was first described in 1829 by the French naturalist Jean Victoire Audouin. The specific epithet honours the French zoologist Marie Jules César Savigny who described many new marine species from the Mediterranean Sea and Red Sea

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