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Colobocentrotus atratus, the helmet urchin or shingle urchin, is a species of sea urchin in the family Echinometridae. In Hawaii it is known as "kaupali" which translates as "cliff-clinging". It is found on wave-swept intertidal shores in the Indo-West Pacific, particularly on the shores of Hawaii.
This urchin is a deep maroon colour and shaped like a domed limpet. It can grow to the size of a softball, but is usually much smaller.
The upper surface is a mosaic of tiny polygonal plates formed from modified spines to form a smooth mosaic. This is fringed by a ring of large, flattened modified spines.
On the underside there is another ring of smaller flattened spines and a large number of tube feet.