Corals are considered to be marine animals and the theory of their formation, first stated by Charles Darwin, is generally accepted. The same scientist is the one that established some a few types of coral, according to different criteria.
According to their reproductive process, there are two types of coral: those which employ sexual reproduction, meaning that the single sex colonies are fecundated by the gametes of the hermaphroditic ones. The other type gathers the corals that reproduce asexually. The colonies multiply by constant division. Some colonies can even reproduce through fragmentation, and this happens when a piece of a coral brakes and continues to develop in another place. According to their geological structure, there are several different types of corals that have been identified by the scientists, among which are the fossil corals, the tabulate corals, the rugose corals or scleractinan corals.
Some of those ancient types of corals still exist deep in the seas whereas others have disappeared throughout time, especially due to environmental changes. Eventually, according to the uses people have attributed to them, the corals fall under two categories. Live corals are those types of corals which are most of the times a good source for fish food, therefore contributing to the growth of economy in some areas, whereas the second category, the ancient corals, are used as building blocks or as research material for scientists. What makes these different types of corals worthy of interest is the fact that they combine usefulness with beauty, and the mistery of their appearance continues to raise questions in the minds of some people, may they be scientists or passionate aquarium owners.
