Rainbow fire urchin

Large urchin belonging to the Diadematidae family, with long and mobile spines. Highly variable colour, from light to dark brown, almost black. Young specimens have banded spines. Always visible 5 areas free from spines, V shaped, bright red with blue spots at the sides. Brown anal sac, dark tipped. 20 cm.
Often found in bay and lagoon, on sandy and rubble bottoms. It often forms aggregations of many specimens, moving together staying in contact. Identifiable from other Diadematidae by the red lines and blue dots.
Often associated with commensal crustaceans, as the crab Zebrida adamsii, the shrimps Periclimenes hirsutus, Stegopontonia commensalis, juvenile cardinal fishes or razor fishes, the juvenile Lutjanus sebae. It lives in symbiosis with the crab Dorippe frascone, carrying the urchin on its back.