David Fleetham / Close-up of Horned helmet shell (Cassis cornuta) hunting Red Pencil Urchin (Heterocentrotus mamillatus), Hawaii, USA, Pacific Ocean.

David Fleetham / Day octopus (Octopus cyanea) releasing an ink cloud to escape predator on reef, as Red pencil urchin (Heterocentrotus mamillatus) rests behind, Hawaii, USA, Pacific Ocean.

David Fleetham / Psychedelic wrasse (Anampses chrysocephalus) juvenile swimming in reef, with Slate pencil sea urchin (Heterocentrotus mammillatus) behind, Hawaii, Pacific Ocean.

David Fleetham / Commerson's frogfish (Antennarius commersoni) juvenile sheltering among spines of Slate pencil sea urchin (Heterocentrotus mammillatus), Hawaii, Pacific Ocean.

David Fleetham / Close up of skin between the spines of a Slate pencil sea urchin (Heterocentrotus mammillatus), Hawaii, Pacific Ocean.

David Fleetham / Three scuba divers swimming over coral reef looking at Slate pencil sea urchins (Heterocentrotus mammillatus), Molokini Marine Preserve, Maui, Hawaii, Pacific Ocean. Model released.

David Fleetham / Red slate pencil urchin shrimp (Levicaris mammillata) sitting on the spine of a Red slate pencil urchin (Heterocentrotus mamillatus), Hawaii, Pacific Ocean.

David Fleetham / Slate pencil sea urchin (Heterocentrotus mammillatus), close up view between its spines, Hawaii, Pacific Ocean.

David Fleetham / Yellowmargin moray eel (Gymnothorax flavimarginatus) sheltering in a crevice behind a Slate pencil sea urchin (Heterocentrotus mammillatus), Hawaii, Pacific Ocean.

David Fleetham / Slate pencil sea urchin (Heterocentrotus mammillatus) using its spines to attach to a rock crevice, Hawaii, Pacific Ocean.

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

David Fleetham / Slate pencil sea urchins (Heterocentrotus mammillatus) on a reef, with two swimmers free diving in background, Molokini Marine Preserve, Maui, Hawaii, Pacific Ocean.