GEORGETTE DOUWMA / SCIENCE PHOTO LIBRARY GEORGETTE DOUWMA / SCIENCE PHOTO LIBRARY
Sea urchin (Asthenosoma marisrubri). The sea urchin is an echinoderm, a relative of the star fish. Its exoskeleton shell, or test, is covered in spines that protect it from predators. At the end of each spine is a venom filled sac (white). It is found near coral reefs in the Red Sea and can reach diameters of 25 centimetres. It feeds on algae that it scrapes from the surface of rocks. Photographed in the Red Sea, Egypt.
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