4 Different Ocean Animals In 4 Different Ocean Feature Habitats Brittle Stars – Why Are They Brittle?

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Brittle Stars – Why Are They Brittle?

Ocean life includes some hidden wonders which are in the form of dynamic plants and amazing animals. It is not easy to imagine what kind of animals dwell under the waters of the ocean. Animals range in size from microscopic to large whales. One such sea creature that looks quite strange is the brittle star. The brittle star belongs to the kingdom Animalia and the phylum Echinodermata. The order to which brittle stars belong is Ophiuroidea, so they are also called opiuorids. They are closely related to starfish. They have very flexible long arms with the help of which they crawl over the substratum of the sea floor. They have very long wings that can reach up to 60 cm in length and are five in number. They are also known as serpent stars.

They are not easily recognized by people and go unnoticed, but they share a diverse group. About 1,500 types of brittle stars are known today and are usually found at depths below 500 m. Ophiroids are believed to have evolved in the early Ordovician about 500 million years ago. They are adapted to a wide range of marine habitats from the tropics to the poles. They are also found attached to coral reefs and some species are also known to tolerate brackish water, their exoskeleton is made up of bones. There are about 1900 extant species and 230 genera of brittle stars divided into three orders which include Oegophiurida, Phrynophiurida and Ophiurida. Sthenurida is an order of the Paleozoic era and is extinct.

Like all echinoderms, ophiuroids have a strong tendency toward pentaradial symmetry. The outline of the body of brittle stars is similar to that of starfish in that all five arms are attached to the central disc with a slight difference that all arms are not fully attached to the central disc. This central disk contains all the organs of the body and the various organs do not enter the wings as they are found in starfish. The lower part of the central disk closes the mouth surrounded by five jaws composed of skeletal plates. Madreporite is present in the middle of any of the jaw plates and present on the lower side, but in starfish it is present on the upper side.

The water vascular system is very well marked in brittle stars as it is the characteristic feature of echinoderms. The vascular system of water provides force for movement. The tube feet are the terminations of the water vascular system. Usually a madreporite is present in the water vascular system, but species also lack a madreporite. Suckers and ampoules are missing from the legs of the brittle star tube. The nervous system is very simple and consists of a main nerve ring that sends fine nerves along the wings. The exact location of the nerve ring is in the central disc. Sensory organs are not well developed. They also lack eyes. The nerve endings of the nerve ring perform the work of touch, taste, etc.

The mouth of the brittle star is surrounded by five jaws which perform the function of the anus as well as the mouth which serves both for swallowing and for swallowing food. Just behind the jaws is the esophagus and a blind stomach. Digestion progresses in the stomach pouches and the stomach wall contains hepatic cells. Ophiuroids are considered essentially scavengers or detritivores and small food particles are carried towards the mouth with the help of tube feet. Sometimes they also feed on crustaceans and small worms. The bases of the wings contain cilia-lined sacs called bursae that are used for gas exchange. The cells present in the bursa are the main source for the movement of oxygen-rich water currents, which circulate through the water vascular system. Bursae are also secretory organs as they contain phagocytic cells that participate in the removal of waste from the body. The exoskeleton of ophiuroids is composed of calcium carbonate like all echinoderms which is present in the form of calcite. The calcite ossicles fuse together to form plates which are later covered by the epidermis, taking the form of syncytium. Generally, the sexes are separate, but some species are also hermaphrodites. Gametes are stored in sacs located in the wings and are released through the bursa. Fertilization is external and the gametes are shed into the surrounding water. A few species are also viviparous and show parental care by developing their immature larvae in bursae. A few females of some species carry a dwarf male permanently attached to his mouth.

Brittle stars reach maturity in two years and are fully grown in about three to four. Their average lifespan is only five years, but some species can even live longer than that. They have great powers of regeneration also called autotomy. Autotomy is the defense process in which ophiroids break off one of their wings when attacked by a predator and flee. This lost arm is later created by the regeneration process. They move with the help of their wings which lack suckers. They are also attacked by parasites, which include protozoa, nematodes, algae, etc. Although they are non-toxic, they are not used as food by humans. They are used by fish as part of the aquarium.

Fragile stars are very cool as they are generally not noticed by predators.

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