Starfishes (Asteroidea), are an exclusively marine class within the Echinoderms, which are characterized by having a somewhat flattened and flexible body formed by a central disk to which they gradually radiate 5 or more arms. On the ventral side is the mouth, located in the center of the central pentagon-shaped disc. Radiating from the mouth to the ends of the arms, we can observe a channel in which we find structures called ambulatory feet. It is frequent that the ambulacral feet are protected by movable spines. The function that fulfills the ambulacral feet, is not only locomotive (starfishes make slow movements), but also they are used like sensorial structures. On the side of the body opposite to the mouth, the aboral side, it is usually rough and even in certain species spiny. Some of these species, their spines have been flattened, thus providing a smooth surface.
It is important to note that starfishes have the ability to regenerate, being able to reconstitute arms that the animal may have lost, generally because of a predator.
Starfishes are distributed throughout the seas of the world. They generally frequent rocky or hard bottoms, although there are also species that bury themselves and dig the sandy/muddy bottoms. They are common in coastal waters, where they can aggregate in considerable numbers on rocks. Generally their bodies are brightly colored. Their sizes are variable, with species barely exceeding 1 centimeter in diameter, and others that can reach up to 1 meter in diameter.
Starfishes are mostly predatory species of sedentary prey. They can feed on Molluscs (oysters and clams), Crustaceans and other invertebrates. There are also species that feed on organic particles in suspension. The case of Acanthaster planci or crown of thorns star is known to be a natural species of coral reefs, where it feeds on coral polyps. This species is a danger, when the number of specimens is out of control, and can cause serious damage to the reefs.
Currently there are about 1,500 species of starfishes in our seas.