Pascal Kobeh / Reef covered with two red Stomphia sea anemones (Stomphia coccinea), with Plumose anemones (Metridium senile), Red soft corals (Eunephthya / Gersemia rubiformis) and Green sea urchins (Strongylocentro...

Pascal Kobeh / Atlantic / Common rock crab (Cancer irroratus) on the reef in the middle of green sea urchins (Strongylocentrotus droebachiensis) Gulf of Saint Lawrence, Canada

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis). Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis), three of different colours. Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis) mouth and spines, close up. Tenerife, Canary Islands.

Sergio Hanquet / Mass of Purple sea urchins (Sphaerechinus granularis) high numbers may be related reproduction cycle. Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchins (Sphaerechinus granularis), high numbers may be related reproduction cycle. Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis) many on seabed, high numbers may be related reproduction cycle. Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis). Tenerife, Canary Islands.

Sergio Hanquet / Purple sea urchin (Sphaerechinus granularis). Tenerife, Canary Islands.

SCOTLAND: The Big Picture / Horse mussel bed (Modiolus modiolus) with Brittle stars (Ophiothrix fragilis),Edible crab (Cancer pagurus) and Northern sea urchin (Strongylocentrotus droebachiensis) Sheltand Islands, Scotland, UK, S...

SCOTLAND: The Big Picture / Edible sea urchins (Echinus esculentus) grazing under a kelp forest, Scotland, UK, October.

SCOTLAND: The Big Picture / Edible sea urchin (Echinus esculentus), Shetland Isles, Scotland, UK, MAy.

Pascal Kobeh / Sea urchin (Sphaerechinus granularis) Azores, Atlantic ocean.

Sue Daly / Edible sea urchin (Echinus esculentus), Trondheimsfjord, Norway, July.

Sue Daly / Edible sea urchin (Echinus esculentus), Trondheimsfjord, Norway, July.

Sue Daly / White sea urchin (Echinus acutus), Trondheimsfjord, Norway, July.

Sue Daly / Reef wall with Edible sea urchin (Echinus esculentus) and Dead man's fingers soft coral (Alcyonium digitatum), Isle of Man, July.

Olga Kamenskaya / Purple sea urchin (Strongylocentrotus purpuratus) off the coast of Svalbard, Norway. September.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on white background, collected in Greece.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on sand, Greece.

Nick Upton / Purple sea urchin (Sphaerechinus granularis) shell on sand, Greece.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on white background, collected in Greece.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on sand, Greece.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on sand, Greece.

Nick Upton / Violet / Stony / Rock sea urchin (Paracentrotus lividus) shell on sand, Greece.

Nick Upton / Green sea urchin (Psammechinus miliaris) in a rockpool, Cornwall, England, UK, September.

Constantinos Petrinos / Collector urchin (Tripneustes gratilla) detail close up, Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Urchin bumblebee shrimp (Gnathophyllides mineri) living commensally with Collector Urchin (Tripneustes gratilla), close up. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Urchin bumblebee shrimp (Gnathophyllides mineri) living commensally with Collector Urchin (Tripneustes gratilla), close up. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Urchin bumblebee shrimp (Gnathophyllides mineri) living commensally with Collector Urchin (Tripneustes gratilla), close up. Lembeh Strait, North Sulawesi, Indonesia.

Constantinos Petrinos / Urchin bumblebee shrimp (Gnathophylloides mineri) living commensally with Collector Urchin (Tripneustes gratilla), close up. Lembeh Strait, North Sulawesi, Indonesia.

Sue Daly / Close-up of a Common sea urchin (Echinus esculentus) showing spines and tube feet, Sark, British Channel Islands, UK, 2013.

Sue Daly / Common sea urchin (Echinus esculentus) attached to a wall, with female Cuckoo wrasse (Labrus mixtus) swimming in the background, Sark, British Channel Islands, UK, 2013.

Solvin Zankl / Red / Edible Chile sea urchin (Loxechinus albus) on Lampshell (Magellania venosa) Comau Fjord, Patagonia, Chile, Atlantic Ocean

Alex Mustard / A view through Kelp forest (Laminaria hyperborea) with Common sea urchins (Echinus esculentus) grazing on the algae, Farne Islands, Northumberland, UK, North Sea, August

Tony Wu / Flower urchin (Toxopneustes pileolus) hard interior shell or test, Kannoura, Toyo-cho, Kochi-ken, Shikoku, Japan.

Franco Banfi / Purple sea urchin (Strongylocentrotus purpuratus) Little Strytan dive site, Eyjafjordur nearby to Akureyri, northern Iceland, North Atlantic Ocean.

Pascal Kobeh / Colony of Red sea urchins (Strongylocentrotus franciscanus) at the feet of Bull kelps (Nereocystis luetkeana) Vancouver Island, British Columbia, Canada. Pacific Ocean.

Franco Banfi / Sea urchin (Sphaerechinus granularis), Larvotto Marine Reserve, Monaco, Mediterranean.

Franco Banfi / Sea urchin (Sphaerechinus granularis) on coral covered with mucilage, a symptom of rising sea temperature, Vis Island, Croatia, Adriatic Sea, Mediterranean.

Franco Banfi / Giant red sea urchin (Strongylocentrotus franciscanus) Vancouver Island, British Columbia, Canada, Pacific Ocean

Solvin Zankl / Deepsea Sea urchin (Dermechinus horridus) specimen from the Scotia Sea, Southern Atlantic Ocean, near South Georgia Island.

Pete Oxford / Galapagos green sea urchin (Lytechinus semituberculatus) Galapagos. Endemic.

Georgette Douwma / Collector urchin (Tripneustes gratilla)Debris tends to 'collect' on these urchins, hence their name. Mabul, Malaysia. Indo-Pacific.

Michael Hutchinson / Cape sea urchin (Parechinus angulosus) and Mediterranean mussels (Mytilus galloprovincialis) on rock, Cape Province, South Africa, December.

Michael Hutchinson / Cape sea urchin (Parechinus angulosus) on rock, Cape Province, South Africa, December.

Pascal Kobeh / Flower urchin (Toxopneustes pileolus), a poisonous sea-urchin, New Caledonia, Pacific Ocean.

Pascal Kobeh / Collector urchin (Tripneustes gratilla), New Caledonia, Pacific Ocean.

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

Richard Robinson / White sea urchin (Pseudechinus huttoni) in Doubtful Sound, Fiordland National Park, New Zealand..

Richard Robinson / White sea urchin (Pseudechinus huttoni) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / White sea urchin (Pseudechinus huttoni) in Doubtful Sound, Fiordland National Park, New Zealand.

Richard Robinson / Kina, sea urchin (Evechinus chloroticus) in Breaksea Sound, Fiordland National Park, New Zealand.

Pascal Kobeh / Underwater reef covered with a colony of Red sea urchins (Strongylocentrotus franciscanus), Alaska, USA, Gulf of Alaska. Pacific ocean.

Pascal Kobeh / Poisonous sea urchin (Toxopneustes pileolus / roseus) can be lethal if touched, Baja California peninsula, Mexico. Sea of Cortez.

Pascal Kobeh / Two Stimpson's snapping shrimps (Synalpheus stimpsoni) in a crinoid / feather star, Manado, Indonesia. Sulawesi Sea.

Sue Daly / Common sun star (Crossaster papposus) Velvet Swimming Crab (Necora puber) and Common Sea Urchin (Echinus esculentus) St Abbs Voluntary Marine Reserve, Scotland (North Sea).

Sue Daly / Close up of Common Sea Urchin (Echinus esculentus) showing tube feet, St Abbs Voluntary Marine Reserve, Scotland (North Sea).

Sue Daly / Close up of Common Sea Urchin (Echinus esculentus) showing tube feet, St Abbs Voluntary Marine Reserve, Scotland (North Sea).

Sue Daly / Common Sea Urchin (Echinus esculentus) St Abbs Voluntary Marine Reserve, Scotland (North Sea).

Sue Daly / Mouth of Common Sea Urchin (Echinus esculentus) Guillaumesse, Sark, British Channel Islands.

Sue Daly / Mouth of Common Sea Urchin (Echinus esculentus) Guillaumesse, Sark, British Channel Islands.

Sue Daly / Common Sea Urchin (Echinus esculentus) Guillaumesse, Sark, British Channel Islands.

Sue Daly / Common Sea Urchin (Echinus esculentus) The Isles of Scilly.

Sue Daly / Common Sea Urchin (Echinus esculentus) Guillaumesse, Sark, British Channel Islands.

Solvin Zankl / Sea urchin (Evechinus chloroticus) Poor Knights Islands, Marine Reserve, New Zealand, South Pacific Ocean, July.

Claudio Contreras / Mexican hogfish (Bodianus diplotaenia) juvenile and White sea urchin (Tripneustes depressus), Cabo Pulmo National Park, Sea of Cortez (Gulf of California), Mexico, July

Franco Banfi / Scuba diver and Sea urchin (Echinus melo) Ponza Island, Italy, Tyrrhenian Sea, Mediterranean

Georgette Douwma / Cake urchin (Tripneustes gratilla) Cebu, Malapascua Island, Philippines, September

Georgette Douwma / Cake urchin (Tripneustes gratilla) Cebu, Malapascua Island, Philippines, September

Georgette Douwma / Flower urchin (Toxopneustes pileolus) extremely venomous, the long feet attach debris for camouflage, Cebu, Malapascua Island, Philippines, September

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.

Terry Whittaker / Tracking shot of Arctic fox (Vulpes lagopus) male walking along rocky beach with Green sea urchin (Strongylocentrotus droebachiensis) in mouth, Hornstrandir Nature Reserve, Iceland. February.

Russell Laman / California sea lions (Zalophus californianus) swimming over rock covered in Bat stars (Patiria miniata) and Pacific purple sea urchins (Strongylocentrotus purpuratus) near the Monterey Coast Guard Pie...

Russell Laman / Giant spined star (Pisaster giganteus) on a rock alongside Pacific purple sea urchins (Strongylocentrotus purpuratus) underneath a Giant kelp (Macrocystis pyrifera) forest off the coast of Monterey, C...

Russell Laman / Pacific purple sea urchins (Strongylocentrotus purpuratus) feeding on Giant kelp (Macrocystis pyrifera) on seabed, Monterey, California, USA, Pacific Ocean.

Russell Laman / Pacific purple sea urchins (Strongylocentrotus purpuratus) and Strawberry anemones (Actinia fragacea) covering rocks on seabed, Monterey, California, USA, Pacific Ocean.

Russell Laman / California sea lions (Zalophus californianus) swimming over rocks covered in Pacific purple sea urchins (Strongylocentrotus purpuratus) and Strawberry anemones (Actinia fragacea), Monterey, California...

Joel Sartore / Photo Ark / Common sea urchin (Heliocidaris erythrogramma) portrait, Melbourne Zoo. Captive, occurs in western Pacific Ocean.

Joel Sartore / Photo Ark / Common sea urchin (Heliocidaris erythrogramma) portrait, Melbourne Zoo. Captive, occurs in western Pacific Ocean.

Tui De Roy / Two Chocolate chip seastars (Nidorellia armata) with Green sea urchin (Lytechinus variegatus) on sea floor, Galapagos Islands, Ecuador. Pacific Ocean.

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

Shane Gross / Red sea urchins (Strongylocentrotus franciscanus) gathered on the seabed, Barkley Sound, Vancouver Island, British Columbia, Canada.

Shane Gross / Purple sea urchins (Strongylocentrotus purpuratus) and Red sea urchins (Strongylocentrotus franciscanus) on seabed, Barkley Sound, Vancouver Island, British Columbia, Canada.

Shane Gross / Noble dorid (Peltodoris nobilis) resting on rocks surrounded by Sea urchins (Strongylocentrotus sp.) and Orange sea cucumbers (Cucumaria miniata), Barkley Sound, Vancouver Island, British Columbia, Ca...

Shane Gross / Underwater seascape showing Sunflower sea star (Pycnopodia helianthoides), Orange sea cucumbers (Cucumaria miniata) and Sea urchins (Strongylocentrotus sp.), Barkley Sound, Vancouver Island, British C...

Shane Gross / Sea urchins (Strongylocentrotus sp.) feeding on algae growing on a plastic milk crate left on the seabed, Barkley Sound, Vancouver Island, Canada.

Shane Gross / RF - Giant Pacific octopus (Enteroctopus dofleini) camouflaged among rocks with Sea urchins (Strongylocentrotus sp.) and Orange sea cucumbers (Cucumaria miniata), Barkley Sound, Vancouver Island, Brit...

Tony Wu / Male intermediate sea urchin (Strongylocentrotus intermedius) starting process of broadcast spawning. Pacific Ocean, Hokkaido, Japan.

Tony Wu / Male intermediate sea urchin (Strongylocentrotus intermedius) starting process of broadcast spawning. Pacific Ocean, Hokkaido, Japan.

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.

Georgette Douwma / Composite image of echinoderms on black background. Top row from left: Featherstar (Crinoidea), Sea apple (Pseudocolochirus violaceus). Central row from left: Mosaic cushion star (Halityle regu...