Brittle stars or ophiuroids (Ophiuroidea) are the most numerous class within the Echinoderms. Currently there are more than 2,000 species described. Among their characteristics, we find the peculiar pentaradian symmetry of the Echinoderms. Their body, to some degree similar to the evolutionarily close class of Starfishes (Asterids), has a compact and flattened central disk from which five slender and sharp arms radiate, formed by a column of articulated ossicles. The arms can be simple or can even branch out repeatedly along their length. The movement of these animals is carried out by means of undulating movements of their arms. In general, they are animals with dull colors, although there are exceptions with bright and very striking colors.
Brittle stars skin is leathery, and is covered by dermal plates and spines arranged in patterns that are generally specific to the species. The mouth is located on the lower side of the body, and has 5 movable plates that act as jaws. They tend to be reserved species, living in hard substrates where they reach little or no light, so they will be frequent in cervices and cracks, being more easily observed at night. They can be found in many marine habitats, from coastal waters to abyssal plains.
The diet of brittle stars is varied, there are species that feed on small particles, either actively looking for them on the seabed, or filtering them through mucous secretions that trap the particles present in the water column. Other species are carnivorous, having been described a specie that has specialized in capturing small fish thanks to spines present in its arms, with which it captures its prey.
Brittle stars have an even greater capacity for regeneration than Starfishes (Asterids). From an arm or even a fragment of the central disk, they are able to completely regenerate the arms and parts that are missing. Often, brittle stars are able to detach themselves from one of the arms in order to escape from predators.