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.

Gary Bell/ Oceanwide / Hawaiian Sea Urchin (Tripneustes gratilla), Anilao, Philippines

Gary Bell/ Oceanwide / Sea Urchin (Toxopneustes pileolus), Anilao, Philippines

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

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