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The diadema urchin or blue-black urchin (''Echinothrix diadema'') is a species of tropical sea urchin, member of the Diadematidae family. == Description and characteristics == ''Echinothrix diadema'' is a long spined urchin. With its spines, the typical diameter is .〔Florent's Guide To The Tropical Reefs: ''(Blue-Black Urchin. )'' Retrieved 12 September 2014.〕 It is generally black or blue-black in colour, and always dark (the spines show a blue sheen in the light). The spines are closed at the tip; the anal sac is small and dark. It differs from ''Echinothrix calamaris'' in that the spines are not banded, except in juveniles, and that its anal sac is small and hardly visible, and the spines show a blue sheen (whereas dark morphs of ''E. calamaris'' show a greenish tinge). Another similar species is ''Diadema setosum'', which has longer spines and smaller test, the distinguishing feature being an orange ring around anal sac. Image:Echinothrix calamaris, jeune individu.jpg|Young individual Image:Echinothrix diadema Landaagiraavaru.jpg|Older juvenile Image:Echinothrix diadema Réunion.jpg|Adult. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Echinothrix diadema」の詳細全文を読む スポンサード リンク
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