David Fleetham / Close look between the spines of Slate pencil sea urchin (Heterocentrotus mammillatus), Hawaii.

David Fleetham / Slate pencil sea urchins (Heterocentrotus mammillatus) in reef scene, Hawaii.

David Fleetham / Slate pencil sea urchins (Heterocentrotus mammillatus), pennantfish / bannerfish (Heniochus diphreutes) and moorish idols (Zanclus cornutus) on reef, Hawaii.

David Fleetham / Red liomera crab (Liomera rubra) female holding a tail full of eggs in a slate pencil sea urchin (Heterocentrotus mammillatus) at night, Hawaii.

Pascal Kobeh / Slate pencil urchin (Heterocentrotus mamillatus), New Caledonia, Pacific Ocean.

Fred Bavendam / Slate Pencil Urchin (Heterocentrotus mammillatus) pair attached to rock wall, Kona, Hawaii

David Hall / Slate pencil sea urchin {Heterocentrotus mammillatus} Red Sea - nocturnal

Norbert Wu / Slate Pencil Urchin (Heterocentrotus mammillatus) spines are stony and used for wind chimes, Hawaii

Norbert Wu / Pencil Urchin (Ctenocidaris perrieri) and Brittle Star (Ophionotus victoriae) similar to deep sea species, New Harbor, Antarctica

Jeff Rotman / Spines of Slate pencil sea urchin {Heterocentrotus mammilatus} Red Sea.

Jeff Rotman / Slate pencil sea urchin {Heterocentrotus mammillatus} Hawaii, Pacific Ocean

David Fleetham / Whitemouth moray eel (Gymnothorax meleagris) and slate pencil sea urchins (Heterocentrotus mammillatus), Hawaii.