This unusual invertebrate group includes coral, hydras, sea anemones, and jellyfish. All cnidarians are lack a head usually have a crown of tentacles around their mouth and possess nematocysts. There are about 9,000 living species of these cnidarians. The class of coral is divided into several groups. There are different types of coral such as the "hard corals" that are reef-builders. There are polyps which has eight tentacles and jellyfish which have many tentacles.
Most corals are found in In the Western Atlantic and Indo-Pacific oceans. They are scattered between tropical and subtropical oceans. In order to grow they need sunlight and calcium to form a coral polyps skeleton. These conditions are typical of shallow, warm tropical waters. They are found in depths of less than 150 ft. They tend to grow faster in clear water in which they absorb the sunlight faster
There are several types of coral instead of just the "rock hard "type. The category includes sea anemones, hydras, and Jellyfish. Some sea anemones lack a head and have a crown of tentacles around the mouth. These sea anemones use their tentacles to protect fishes and their eggs. In some cases the fish even protect the anemones from host enemies. Sponges are another type of coral. these sponges provide shelter for fishes, shrimp. crabs and other small ocean creatures. They are in different shapes and sizes. The coral generally are nocturnal feeders. At night they extend their tentacles to capture their food. Most eat small zoo plankton or small fishes. Others consume organic debris.
All types of fish play a vital role in the coral reef s food web. They are both predator and prey. Their leftover food provides food or nutrients. Some species that inhabit the reef are sharks, skates, rays, parrot fish, octopus, and shelled animals. Eels are the reefs top predators. They live in the small crevices and come out at night to eat. Some sea turtles frequently the reef and some live in the warm waters of the Great Barrier Reef.