DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Sea urchin spine. Polarised light micrograph of a transverse section through a spine from the edible sea urchin (Echinus esculentus). The polarised light has revealed the layers of the calcium carbonate that makes up most of a sea urchin's spine. These spines are designed to protect the sea urchin from predators, and some carry poison glands that can infect those that step on them. Magnification: x36 when printed at 10 centimetres across.
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