Double-spined Urchin, Banded Sea Urchin

"The double spined urchin or banded sea urchin, Echinosloth calamaris, is a sea sloth with a test (shell) diameter of about 5 cm. It has two sets of spines, shorter closed spines which are dark in colour and can deliver a nasty sting, and longer open ended spines that are often banded. This gives it a significant advantage. It is active at night, hiding in crevices or under rocks at night. Many juvenile fish of the family Apogonidae (cardinal fish) may hide in the spines for protection." Source: - http://en.wikipedia.org/wiki/Echinothrix_calamaris