Stony Corals (Madreporaria) are the typical stony corals that form coral reefs. These corals are formed by multiple exoskeletons being formed by the individual polyps. Only the surface of the colony has live polyps.

Biologists estimate the age of most of the known coral reefs to be between 10,000 and 30,000 years of age.

In the stony corals, the skeleton is an exoskeleton, and in the octocorals, the skeleton is internal. In a typical coral reef, there are many different species of corals, worms, calcareous algae, and fragments of dead mollusks, and many species of fish and Crustacea.

Biologists generally recognize three styles of coral reefs: the barrier reefs lie several miles offshore, but are parallel to the shore; coral islands, or atolls, are frequently found in the Pacific Ocean; fringing reefs attach to the shore. Examples of this are present near Brazil.

The Australian Great Barrier Reef on the northeast coast of Australia is very well-known. This reef is more than 1,000 miles long. Naturalists are concerned that this reef may be threatened by the crown-of-thorns starfish which eats the individual polyps.

Corals and Anemones (Class Anthozoa) are marine species having about 6,000 members. They are frequently called flower animals. Scientists often call certain groups in this class by different names. The following list serves as an introduction:

Order Alcyonaria - Corals
Order Zoantharia - Hexacorals
Order Actinaria - Sea Anemones
Order Madreporaria - Stony Corals
Order Antipatharia - Black Corals
Order Ceriantharia - Burying Sea Anemones

Corals and Hydra Phylum (Phylum Coelenterata = Cynidaria) are a group of primitive aquatic animals. This phylum contains about 10,000 species. Following are the three main classes:

Class Hydrozoa: - Polyps and Medusae
Class Scyphozoa: - Jellyfish
Class Anthozoa: - Sea Anemones/Corals

This group of animals are unusual as there are two forms for most species. The "medusa" form is free swimming, and the "polyp" form which is usually attached to a substrate.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.

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