Echinothrix diadema
species of echinoderm
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 10–20 cm (3.9–7.9 in). The internal organs are enclosed in the test, covered by a thin dermis and epidermis. 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.
Feeding habits
The grazing preferences of Echinothrix diadema in Fiji were found to correlate with its preferred algae/seagrass species, Codium geppiorum. The grazing activity contributes to echinoid bioerosion.
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This entry incorporates text from “Echinothrix diadema” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.