Shelves of coral surround the Pacific island of Palau. Corals, small organisms related to anemones, secrete calcium carbonate, which hardens into an exoskeleton and over time forms reefs.

Coelenterate Coral

Shelves of coral surround the Pacific island of Palau. Corals, small organisms related to anemones, secrete calcium carbonate, which hardens into an exoskeleton and over time forms reefs.
Photograph by Tim Laman, National Geographic

Coral Kingdoms

See coral kingdom photos, from National Geographic

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