Updated 1 January 2020
Corals are marine invertebrates in the class Anthozoa of the phylum Cnidaria, the phylum that also includes jellyfish and sea anemones. A handful of coral species live in relatively cold water, but the vast majority grow in warm, tropical oceans. Corals can live on their own, but primarily live in colonies of up to thousands of individual coral animals, called polyps, which are all genetically identical clones to each other.
These colonies are how we generally picture coral––spectacular reefs of brightly-colored limestone structures. In fact, however, the corals themselves are without color and translucent, or partially see-through. The different colors we associate with corals and coral reefs come from the zooxanthellae algae that live inside the polyps in symbiosis, meaning that the corals offer protection to the algae and in turn absorb some of the nutrients the algae produce through photosynthesis. Aside from that, the corals themselves are in fact carnivores, using small, venomous tentacles with special stinging cells known as cnidocytes to paralyze and consume small marine animals.
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