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Coral
Coral. Close-up of a hard coral (Tubastrea sp.). Corals consist of colonies of individual animals called polyps. The polyps are simple creatures, with a ring of tentacles leading to a gullet. The tentacles have nematocysts (stinging cells) that are used to catch small prey as they swim past. Once stung the prey is moved to the opening of the gullet by the tentacles. The polyp may also feed by filtering zooplankton from the water. Hard corals secrete calcium carbonate, which forms a protective skeleton around the polyps. When the polyp dies the skeleton remains and new polyps grow on top of it, forming a coral reef.
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