Alex Mustard / Hearth heart urchin (Maretia planulata) which usually lives buried in the sand, crawls along the seabed. Dauin, Dumaguete, Negros, Philippines. Bohol Sea, tropical west Pacific Ocean.

Constantinos Petrinos / Longspine heart urchin (Maretia planulata) burrowing into the sand, Lembeh Strait, North Sulawesi, Indonesia.

Sergio Hanquet / Carapace / shell of Sea urchin (Brissus unicolor) Tenerife, Canary Islands.