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 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.

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

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.

Sergio Hanquet / Sea urchin (Paracentrotus lividus) Tenerife, Canary Islands.