Coral polyps behave like nocturnal animals in many ways. They keep their polyps closed and tucked inside the corallite during the day time. At night, they open the polyps and stretch their tentacles out in search of a good meal. The coral polyp has a slit-like mouth which it uses for feeding. This mouth leads to a short, almost straight tube leading into the body cavity. The body wall of a polyp has two layers: the outer layer, called the ectodermis, and the inner layer, called the gastrodermis. These two layers are separated by the mesoglea. The mesoglea has no cells when the polyp is formed, but gradually develops a variety of cells after some growth.

There are tiny, stinging tentacles called nematocysts that surround the mouth. At the very tip of these tentacles are poison-tipped harpoons that the polyp shoots out to catch its food. The food polyps eat is called zooplankton. Zooplanktons are newly hatched worms, crabs, fish, and other tiny creatures.

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