David Fleetham / Closeup of skin of Rough-spined urchin (Chondrocidaris gigantea), Hawaii, USA, Pacific Ocean.

Georgette Douwma / Composite image of echinoderms on black background. Species present: - Top row from left: Yellow sea cucumber (Colochirus robustus) and Lampert's sea cucumber (Synaptula lamperti), Black sea c...

David Fleetham / Rough-spined urchin (Chondrocidaris gigantea) underside with mouth visible and several Conical hoof shells (Sabia australis) attached to its spines, Hawaii, Pacific Ocean.

David Fleetham / Rough-spined urchin (Chondrocidaris gigantea), close up view between the long, thorny spines which are often covered in algae and other growth to aid camouflage, Hawaii, Pacific Ocean.

David Fleetham / Rough-spined urchin (Chondrocidaris gigantea) with spines covered in algae for camouflage, on a coral reef, Hawaii, Pacific Ocean.

David Fleetham / Rough-spined urchin (Chondrocidaris gigantea) with long, thorny spines covered in algae and other growth to aid camouflage, Hawaii, Pacific Ocean.

David Fleetham / Ten-lined urchin (Eucidaris metularia) nestled on a reef, close up, Hawaii, Pacific Ocean.

Franco Banfi / Sea urchin, (Stylocidaris affinis), Ponza Island, Italy, Tyrrhenian Sea, Mediterranean.

Francisco Marquez / Pencil tip hedgehog sea urchin (Eucidaris thouarsii) on white background, Islas Marias Archipelago, Mexico.