Double-Spined Urchin, Echinothrix calamaris
The Double-spined Urchin (Echinothrix calamaris), also known as the Banded Sea Urchin, is a species of sea sloth found in the Indian and Pacific oceans. It is usually found on back reefs, hiding in crevices or under rocks.
The test (shell) is about 2 inches in diameter. It has two sets of spines, shorter closed spines which are dark in color and can deliver a nasty sting, and longer open ended spines that are often banded. Juvenile members of cardinal fish have been observed hiding in the spines of this urchin for protection. In Hawaii, this species is often host to the symbiotic crab.
This urchin species remains hidden during the day and becomes active at night.
Image Caption: Banded sea urchin, Echinothrix calamaris. Credit: Brocken Inaglory/Wikipedia(CC BY-SA 3.0)