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44-455: Ophiomusium is a genus of brittle stars . Species: This Ophiuroidea -related article is a stub . You can help Misplaced Pages by expanding it . Brittle star Subclass Myophiuroidea Matsumoto, 1915 Brittle stars , serpent stars , or ophiuroids (from Latin ophiurus  'brittle star'; from Ancient Greek ὄφις (óphis)  'serpent' and οὐρά (ourá)  'tail'; referring to

88-464: A change in direction is necessary. Over 60 species of brittle stars are known to be bioluminescent . Most of these produce light in the green wavelengths, although a few blue-emitting species have also been discovered. Both shallow-water and deep-sea species of brittle stars are known to produce light. Presumably, this light is used to deter predators . Brittle stars live in areas from the low-tide level downwards. Six families live at least 2 m deep;

132-520: A few species, the female carries a dwarf male, clinging to it with the mouth. Some brittle stars, such as the six-armed members of the family Ophiactidae , exhibit fissiparity (division through fission), with the disk splitting in half. Regrowth of both the lost part of the disk and the arms occur which yields an animal with three large arms and three small arms during the period of growth. The West Indian brittle star, Ophiocomella ophiactoides , frequently undergoes asexual reproduction by fission of

176-462: A radial nerve which runs to the end of the limb. The nerves in each limb run through a canal at the base of the vertebral ossicles. Most ophiuroids have no eyes, or other specialised sense organs. However, they have several types of sensitive nerve endings in their epidermis, and are able to sense chemicals in the water, touch, and even the presence or absence of light. Moreover, tube feet may sense light as well as odors. These are especially found at

220-462: A relatively large cecum. In many species, it is considerably wider than the colon. For some herbivores such as lagomorphs (rabbits, hares, pikas), easily digestible food is processed in the gastrointestinal tract and expelled as regular feces. But in order to get nutrients out of hard to digest fiber, lagomorphs ferment fiber in the cecum and then expel the contents as cecotropes , which are reingested (cecotrophy). The cecotropes are then absorbed in

264-461: A way similar to lizards which deliberately shed the distal part of their tails to confuse pursuers. Moreover, the Amphiuridae can regenerate gut and gonad fragments lost along with the arms. Discarded arms have not been shown to have the ability to regenerate. Brittle stars use their arms for locomotion. Brittle stars move fairly rapidly by wriggling their arms which are highly flexible and enable

308-463: Is 89 days, so theoretically, each brittle star can produce 15 new individuals during the course of a year. Brittle stars generally sexually mature in two to three years, become full grown in three to four years, and live up to five years. Members of Euryalina , such as Gorgonocephalus , may live much longer. Ophiuroids can readily regenerate lost arms or arm segments unless all arms are lost. Ophiuroids use this ability to escape predators , in

352-407: Is called the ileocecal orifice. The connection between the end of the cecum and the beginning of the ascending colon is called the cecocolic orifice. A cecal carcinoid tumor is a carcinoid tumor of the cecum. An appendiceal carcinoid tumor (a carcinoid tumor of the appendix) is sometimes found next to a cecal carcinoid. Neutropenic enterocolitis (typhlitis) is the condition of inflammation of

396-460: Is made up of embedded ossicles . Of all echinoderms, the Ophiuroidea may have the strongest tendency toward five-segment radial (pentaradial) symmetry . The body outline is similar to that of starfish , in that ophiuroids have five arms joined to a central body disk. However, in ophiuroids, the central body disk is sharply marked off from the arms. The disk contains all of the viscera. That is,

440-478: Is omnivorous and feeds on algae, polychaetes and detritus. In basket stars , the arms are used to sweep food rhythmically to the mouth. Ophiopsammus maculata consumes Nothofagus pollen in the New Zealand fjords (since those trees hang over the water). Eurylina clings to coral branches to browse on the polyps . Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens between

484-755: The Agrio Formation of Neuquén Basin in the 2010s no fossil brittle star was known in the Southern Hemisphere , nor was any brittle star of Cretaceous age known. Silurian fossils from a minor mass extinction called the Mulde event shows the ancestors of modern brittle stars went though a bottleneck, where a miniaturization caused by paedomorphosis led to structural simplification of their skeletal anatomy. These traits affected their further evolution. As they began to increase in size again, so did their complexity. The first large-sized modern brittle star originated in

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528-593: The Early Ordovician . Ophiuroids can be found today in all of the major marine provinces, from the poles to the tropics. Basket stars are usually confined to the deeper parts of this range; Ophiuroids are known even from abyssal (>6,000 m) depths. However, brittle stars are also common members of reef communities, where they hide under rocks and even within other living organisms. A few ophiuroid species can even tolerate brackish water , an ability otherwise almost unknown among echinoderms. A brittle star's skeleton

572-513: The Paleozoic era, brittle stars had open ambulacral grooves, but in modern forms, these are turned inward. In living ophiuroids, the vertebrae are linked by well-structured longitudinal muscles . Ophiuroida moves horizontally, and Euryalina species moves vertically. The latter have bigger vertebrae and smaller muscles. They are less spasmodic, but can coil their arms around objects, holding on even after death. These movement patterns are distinct to

616-408: The cellulose . In humans, the cecum is involved in absorption of salts and electrolytes and lubricates the solid waste that passes into the large intestine. The cecum and appendix are derived from the bud of cecum that forms during week six in the midgut next to the apex of the umbilical herniation. Specifically, the cecum and appendix are formed by the enlargement of the postarterial segment of

660-407: The ileum , and connects to the ascending colon of the large intestine . It is separated from the ileum by the ileocecal valve (ICV), also called Bauhin's valve. It is also separated from the colon by the cecocolic junction. While the cecum is usually intraperitoneal, the ascending colon is retroperitoneal . In herbivores , the cecum stores food material where bacteria are able to break down

704-404: The small intestine and the cecum was not fully understood. Most of the studies of the digestive tract were done on animals and the results were compared to human structures . The junction between the small intestine and the colon, called the ileocecal valve , is so small in some animals that it was not considered to be a connection between the small and large intestines. During a dissection,

748-465: The water vascular system end in tube feet . The water vascular system generally has one madreporite. Others, such as certain Euryalina, have one per arm on the aboral surface. Still other forms have no madreporite at all. Suckers and ampullae are absent from the tube feet. The nervous system consists of a main nerve ring which runs around the central disk. At the base of each arm, the ring attaches to

792-548: The Early Carboniferous. Brittle stars are not used as food, though they are not toxic, because of their strong skeleton. Even if some species have blunt spines, no brittlestar is known to be dangerous, nor venomous. There is no harm evidence towards humans, and even with their predators, brittlestars' only means of defense is escaping or discarding an arm. Brittle stars are a moderately popular invertebrate in fishkeeping . They can easily thrive in marine tanks; in fact,

836-445: The animals to make either snake-like or rowing movements. However, they tend to attach themselves to the sea floor or to sponges or cnidarians, such as coral. They move as if they were bilaterally symmetrical, with an arbitrary leg selected as the symmetry axis and the other four used in propulsion. The axial leg may be facing or trailing the direction of motion, and due to the radially symmetrical nervous system, can be changed whenever

880-463: The arm bases on the underside of the disk. Typically ten bursae are found, and each fits between two stomach digestive pouches. Water flows through the bursae by means of cilia or muscular contraction. Oxygen is transported through the body by the hemal system , a series of sinuses and vessels distinct from the water vascular system. The bursae are probably also the main organs of excretion, with phagocytic "coelomocytes" collecting waste products in

924-411: The arms. The stomach wall contains glandular hepatic cells. Ophiuroids are generally scavengers or detritivores . Small organic particles are moved into the mouth by the tube feet. Ophiuroids may also prey on small crustaceans or worms. Basket stars in particular may be capable of suspension feeding, using the mucus coating on their arms to trap plankton and bacteria. They extend one arm out and use

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968-417: The body cavity and then migrating to the bursae for expulsion from the body. Like all echinoderms, the Ophiuroidea possess a skeleton of calcium carbonate in the form of calcite . In ophiuroids, the calcite ossicles are fused to form armor plates which are known collectively as the test . The plates are covered by the epidermis , which consists of a smooth syncytium . In most species, the joints between

1012-542: The cecum, primarily caused by bacterial infections. Over 99% of the bacteria in the gut are anaerobes , but in the cecum, aerobic bacteria reach high densities. A cecum is present in most amniote species, and also in lungfish , but not in any living species of amphibian . In reptiles , it is usually a single median structure, arising from the dorsal side of the large intestine. Birds typically have two paired ceca, as do, unlike other mammals, hyraxes . Parrots do not have ceca. Most mammalian herbivores have

1056-419: The colon could be traced from the rectum , to the sigmoid colon , through the descending , transverse , and ascending sections. The cecum is an end point for the colon with a dead-end portion terminating with the appendix . The connection between the end of the small intestine (ileum) and the start (as viewed from the perspective of food being processed) of the colon (cecum) is now clearly understood, and

1100-406: The disk with subsequent regeneration of the arms. In both summer and winter, large numbers of individuals with three long arms and three short arms can be found. Other individuals have half a disk and only three arms. A study of the age range of the population indicates little recruitment and fission is the primary means of reproduction in this species. In this species, fission appears to start with

1144-561: The disk, and open into pouches between the arms, called genital bursae. Fertilization is external in most species, with the gametes being shed into the surrounding water through the bursal sacs. An exception is the Ophiocanopidae, in which the gonads do not open into bursae and are instead paired in a chain along the basal arm joints. Many species brood developing larvae in the bursae, effectively giving birth to live young. A few, such as Amphipholus squamata , are truly viviparous , with

1188-471: The embryo receiving nourishment from the mother through the wall of the bursa. However, some species do not brood their young, and instead have a free-swimming larval stage. Referred to as an ophiopluteus , these larvae have four pairs of rigid arms lined with cilia . They develop directly into an adult, without the attachment stage found in most starfish larvae. The number of species exhibiting ophiopluteus larvae are fewer than those that directly develop. In

1232-428: The ends of their arms, detecting light and retreating into crevices. The mouth is rimmed with five jaws, and serves as an anus ( egestion ) as well as a mouth ( ingestion ). Behind the jaws is a short esophagus and a stomach cavity which occupies much of the dorsal half of the disk. Digestion occurs within 10 pouches or infolds of the stomach, which are essentially ceca , but unlike in sea stars, almost never extend into

1276-421: The genera Ophiura , Amphiophiura , and Ophiacantha range below 4 m. Shallow species live among sponges, stones, or coral, or under the sand or mud, with only their arms protruding. Two of the best-known shallow species are the green brittle star ( Ophioderma brevispina ), found from Massachusetts to Brazil, and the common European brittle star ( Ophiothrix fragilis ). Deep-water species tend to live in or on

1320-499: The internal organs of digestion and reproduction never enter the arms, as they do in the Asteroidea. The underside of the disk contains the mouth, which has five toothed jaws formed from skeletal plates. The madreporite is usually located within one of the jaw plates, and not on the upper side of the animal as it is in starfish. The ophiuroid coelom is strongly reduced, particularly in comparison to other echinoderms. The vessels of

1364-455: The latter's increased diameter. The term cecum comes from Latin (intestinum) caecum , literally 'blind intestine', in the sense 'blind gut' or ' cul de sac '. It is a direct translation from Ancient Greek τυφλὸν ( ἔντερον ) typhlòn ( énteron ). Thus the inflammation of the cecum is called typhlitis. In dissections by the Greek philosophers , the connection between the ileum of

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1408-401: The micro brittle star is a common "hitchhiker" that will propagate and become common in almost any saltwater tank, if one happens to come along on some live rock . Larger brittle stars are popular because, unlike Asteroidea, they are not generally seen as a threat to coral, and are also faster-moving and more active than their more archetypical cousins. Cecum It receives chyme from

1452-405: The midgut loop. The proximal part of the bud grows rapidly to form the cecum. The lateral wall of the cecum grows much more rapidly than the medial wall, with the result that the point of attachment of the appendix comes to lie on the medial side. The cecum's position changes after the midgut rotates and the ascending colon elongates, and the accumulation of meconium inside the cecum may result in

1496-617: The ossicles and superficial plates allow the arm to bend to the side, but cannot bend upwards. However, in the basket stars , the arms are flexible in all directions. Both the Ophiurida and Euryalida (the basket stars) have five long, slender, flexible, whip-like arms, up to 60 cm in length. They are supported by an internal skeleton of calcium carbonate plates referred to as vertebral ossicles. These " vertebrae " articulate by means of ball-and-socket joints , and are controlled by muscles. They are essentially fused plates which correspond to

1540-551: The other four as anchors. Brittle stars will eat small suspended organisms if available. In large, crowded areas, brittle stars eat suspended matter from prevailing seafloor currents. Many species in the family Ophiuridae are carnivorous. Ophiura Linnaeus hunts epibenthic animals and the Antarctic Ophiosparte gigas is an active predator. Ophiura albida Forbes and Ophiura sarsii Lütken eat both infaunal prey, carrion and seafloor organic matter, and Ophionereis reticulata

1584-458: The parallel ambulacral plates in sea stars and five Paleozoic families of ophiuroids. In modern forms, the vertebrae occur along the median of the arm. The ossicles are surrounded by a relatively thin ring of soft tissue, and then by four series of jointed plates, one each on the upper, lower, and lateral surfaces of the arm. The two lateral plates often have a number of elongated spines projecting outwards; these help to provide traction against

1628-589: The sea floor or adhere to coral, urchins, or xenophyophores . The most widespread species is the long-armed brittle star ( Amphipholis squamata ), a grayish or bluish, strongly luminescent species. The main parasite to enter the digestive tract or genitals are protozoans. Crustaceans, nematodes, trematodes, and polychaete annelids also serve as parasites. Algal parasites such as Coccomyxa ophiurae cause spinal malformation. Unlike in sea stars and sea urchins, annelids are not typical parasites. Between 2,064 and 2,122 species of brittle stars are currently known, but

1672-552: The sediment leaving only their arms in the stream to capture the plankton). There are also 344 species in the family of Ophiuridae . List of families according to the World Register of Marine Species , following O'Hara 2017: The first known brittle stars date from Early Ordovician . Study of past distribution and evolution of brittle stars has been hampered by the tendency of dead brittle stars to disarticulate and scatter, providing poor brittle star fossils. Until discoveries in

1716-609: The serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea , closely related to starfish . They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens. The Ophiuroidea contain two large clades , Ophiurida (brittle stars) and Euryalida (basket stars). Over 2,000 species of brittle stars live today. More than 1,200 of these species are found in deep waters, greater than 200 m deep. The ophiuroids diverged in

1760-417: The small intestine to utilize the nutrients. In contrast, obligate carnivores , whose diets contain little or no plant matter, have a reduced cecum, which is often partially or wholly replaced by the appendix . Mammalian species which do not develop a cecum include raccoons , bears , and the red panda . Many fish have a number of small outpockets, called pyloric ceca , along their intestine; despite

1804-427: The softening of one side of the disk and the initiation of a furrow. This deepens and widens until it extends across the disk and the animal splits in two. New arms begin to grow before the fission is complete, thus minimizing the time between possible successive divisions. The plane of fission varies so that some newly formed individuals have existing arms of different lengths. The time period between successive divisions

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1848-450: The substrate while the animal is moving. The spines, in ophiuroids, compose a rigid border to the arm edges, whereas in euryalids they are transformed into downward-facing clubs or hooklets. Euryalids are similar to ophiurids, if larger, but their arms are forked and branched. Ophiuroid podia generally function as sensory organs. They are not usually used for feeding, as in Asteroidea . In

1892-453: The taxa, separating them. Ophiuroida moves quickly when disturbed. One arm presses ahead, whereas the other four act as two pairs of opposite levers, thrusting the body in a series of rapid jerks. Although adults do not use their tube feet for locomotion, very young stages use them as stilts and even serve as an adhesive structure. The sexes are separate in most species, though a few are hermaphroditic or protandric . The gonads are located in

1936-448: The total number of modern species may be over 3,000. This makes brittle stars the most abundant group of current echinoderms (before sea stars). Around 270 genera are known, these are distributed in 16 families, which makes them at the same time a relatively poorly diversified group structurally, compared with the other echinoderms. For example, 467 species belong to the sole family of Amphiuridae (frail brittle stars which live buried in

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