What are Coral Polyps?
The marine creatures who form coral reefs and atolls are called coral polyps and they could be as minute as 2.5 centimeters in diameter, while some measure up to 30 centimeters in diameter. As tiny as they are, they have a mouth-like opening at one end of their hollow cylindrical body; said opening is surrounded by even tinier tentacles. The other end is equipped with natural substances allowing these polyps to attach their body to the ocean floor.
Some snorkel and scuba divers who have had the opportunity to go near a coral reef, find it difficult to single out a coral polyp. Reefs are inhabited by about 3,000 species of aquatic organisms, including the communities of coral polyps. These polyps largely resemble other soft-bodied animals because they belong to the Cnidarian family, which include hydras, hydroids, sea fan, sea anemones, and jellyfish.
As living creatures, they feed on the larvae of shellfish organisms, but they subsist largely on algae. One of the unusual facts about corals is that the algae exist right in the polyp’s own tissues. While attached to the polyp, the alga secretes chemical nutrients that enable the coral animals to form external limestone skeletons and develop color.
Inasmuch as the algae are basically plant organisms, they require sunlight in order to perform their food production function by way of photosynthesis. As host to the algae, the polyp tends to assume the alga's color as a living organism.
Another vital substance needed by coral animals to develop their external skeletal formations are the calcium intakes they get from seawater. This is quite important once the polyps go into the process of forming their colonies and develop into a large formation commonly known as corals.