WikipediaRead full entry
The diadema urchin or blue-black urchin (Echinothrix diadema) is a long spined urchin from reefs in the Indo-Pacific, including Hawaii. With its spines, the typical diameter is 10–20 cm (3.9–7.9 in). It is generally black or blue-black in colour, and always dark. The spines are closed at the tip; the anal sac is spotted light and dark.
It is active at night, hiding in crevices or under rocks during the day.
It hosts commensal species like the shrimp Stegopontonia commensalis. Saron marmoratus stays close for protection, like many fish of the families Apogonidae (cardinalfish) and Centriscidae (razorfish and relatives).
It differs from Echinothrix calamaris in that the spines are not banded, except in juveniles. Another similar species is Diadema setosum, which has longer spines, the distinguishing feature being the colour of the anal sac.
|This article about a sea urchin is a stub. You can help Wikipedia by expanding it.|