Coral: some people consider it the cities of the sea. These corals are the homes for many tiny creatures called coral polyps. These coral polyps are no bigger than a human fingernail.

        Most reef corals thrive in water with temperatures that stay between 77 and 85 degrees. Four factors control coral reefs' growth:1 temperature of water;2 amount of salt in water;3 the amount of light that reaches the coral;4 and the coral polyps food supply. 

        Coral colonies usually grow close to the ocean's surface.  There is such a variety of coral species that they create the appearance of an under sea garden. 

        The classic differences between plant and animal life are not always clear in the world of coral.  despite its branch-like appearance, the sea plume (below) belongs to one of the most primitive types