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Brittle Star Fossil range: Ordovician to Holocene
"Ophiodea" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom: Animalia Phylum: Echinodermata Subphylum: Asterozoa Class: Ophiuroidea Gray, 1840
Orders
ME Oegophiurida Ophiurida Phrynophiurida Image File history File links Question_book-3. ... Artist impression of the Ordovician Sea. ... The Holocene epoch is a geological period, which began approximately 11,550 calendar years BP (about 9600 BC) and continues to the present. ... Image File history File links Download high-resolution version (2305x3262, 1749 KB) The 10th plate of Ernst Haeckels Kunstformen der Natur (1904), depicting organisms classified as Ophiodea. ... Ernst Haeckel. ... The 8th print, Discomedusae. ... For other uses, see Scientific classification (disambiguation). ... For other uses, see Animal (disambiguation). ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ... Suborders Zeugophiurina Oegophiurida is an order of Ophiuroidea. ... Suborders See text. ... Families Euryalina Ophiomyxina Phrynophiurida is an order of brittle star. ...

Brittle stars are echinoderms, closely related to starfish. They crawl across the sea-floor using their flexible arms as "legs" for locomotion. The ophiuroids generally have five long slender, whip-like arms which may reach up to 60 centimeters (2 feet) in length on the largest specimens. Classes Subphylum Homalozoa Gill & Caster, 1960 Class Homostelea Class Homoiostelea Class Stylophora Gill & Caster, 1960 Class Ctenocystoidea Robison & Sprinkle, 1969 Subphylum Crinozoa Class Eocrinoidea Jaekel, 1899 Class Paracrinoidea Regnéll, 1945 Class Cystoidea von Buch, 1846 Class Blastoidea Class Crinoidea Subphylum Asterozoa Class Ophiuroidea Class Asteroidea Subphylum Echinozoa Helicoplacoidea †  ?Arkarua...

Ophiuroidea contains two large clades, Ophiurida (brittle stars) and Euryalida (basket stars). Many of the ophiuroids are rarely encountered in the relatively shallow depths normally visited by humans, but they are a diverse group. A clade is a term belonging to the discipline of cladistics. ... Suborders See text. ...

There are some 1,500 species of brittle stars living today, and they are largely found in deep waters more than 500 metres (1,650 feet) down.

Range

The ophiuroids diverged in the Early Ordovician, [ca. 500 million years ago] . The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ...

Ophiuroids can be found today in all of the major marine provinces, from the poles to the tropics. In fact, crinoids, holothurians, and ophiuroids live at depths from 16-35 m, all over the world. Basket stars usually confined to the deeper parts of this range. Ophiuroids are known even from abyssal (>6000 m) depths. However brittle stars are also common, if cryptic, 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 brittles stars skeleton is made up of emmbended ossicles. Subclasses Articulata (540 species) Cladida (extinct) Flexibilia (extinct) Camerata (extinct) Disparida (extinct) Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). ... Orders Subclass Apodacea  Apodida  Molpadiida Subclass Aspidochirotacea  Aspidochirotida  Elasipodida Subclass Dendrochirotacea  Dactylochirotida  Dendrochirotida The sea cucumber is an echinoderm of the class Holothuroidea, with an elongated body and leathery skin. ... Orders Oegophiurida Ophiurida Phrynophiurida Brittle stars are echinoderms, closely related to sea stars. ... metre or meter, see meter (disambiguation) The metre is the basic unit of length in the International System of Units. ... For other uses, see Reef (disambiguation). ... Brackish redirects here. ...

Disc and internal organs

Fossil brittle star Palaeocoma egertoni from the Jurassic of England

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. Photograph of the fossil brittle star Palaeocoma taken by Dlloyd. ... Photograph of the fossil brittle star Palaeocoma taken by Dlloyd. ... Calcium carbonate is a chemical compound, with the chemical formula CaCO3. ...

Of all echinoderms, the Ophiuroidea may have the strongest tendency toward 5-segment radial (pentaradial) symmetry. The body outline is similar to the Asteroidea, in that ophiuroids have five arms joined to a pussy called penus. However, in ophiuroids the central body disk is sharply marked off from the arms. The disk contains all of the viscera. That is, the internal organs of digestion and reproduction never enter the arms, unlike in the Asteroidea. The elaborate patterns on the wings of butterflies are one example of biological symmetry. ...

Green brittle star

The mouth is rimmed with five jaws. Behind the jaws is a short esophagus and a large, blind stomach cavity which occupies much of the dorsal half of the disk. Ophiuroids have neither a head nor an anus. Digestion occurs within 10 pouches or infolds of the stomach. Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens onto the interambulacral area (between the arm bases) of the oral (ventral) surface of the disc. Typically there are 10 bursae, and each fits between two stomach digestive pouches.

The sexes are separate in most species. Gonads in the disc open into the bursae. Gametes are then shed by way of the bursal sacs. Many species actually brood developing larvae in the bursae. The ophiuroid coelom is strongly reduced, particularly in comparison to other echinoderms. 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 a radial nerve which runs to the end of the limb. Ophiuroids have no eyes, as such. However, they have some ability to sense light through receptors in the epidermis.

Micro brittle starfish and Caulerpa racemosa

Both the Ophiurida and Euryalida have five long, slender, flexible whip-like arms, up to 60 centimeters in length. They are supported by an internal skeleton of calcium carbonate plates that referred to as vertebral ossicles. These "vertebrae" articulate through ball-in-socket joints, and are controlled by muscles. The body and arms are also bear calcite plates and delicate spines. Euryalids are similar, 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. Image File history File linksMetadata Download high-resolution version (750x625, 387 KB) Micro brittle starship in aquarist Mike Giangrassos refugium. ... Image File history File linksMetadata Download high-resolution version (750x625, 387 KB) Micro brittle starship in aquarist Mike Giangrassos refugium. ... Species and many others Caulerpa is a genus of seaweeds in the family Caulerpaceae (among the green algae). ...

The vessels of the water vascular system end in tube feet. The water vascular system generally has one madreporite. However, some forms have none. Suckers and ampullae are absent from the tube feet. The water vascular system is a hydraulic system used by echinoderms, such as starfish and sea urchins, for locomotion, food and waste transportation, and respiration[1]. The system is composed of canals connecting numerous tube feet. ... The tube feet can be clearly seen on this sea star Tube feet are the many small tubular projections found most famously on the ventral face of a sea stars arms, but are characteristic of the water vascular system of the echinoderm phylum which also includes sea urchins, sand... Small red or yellow button-like structure that often looks like a small wart on a sea stars central disk. ... The ampulla of Vater is a sphincter (a small muscle) where the common bile duct enters the duodenum. ...

Ophiuroids can readily regenerate lost arms or arm segments unless all arms are lost. Ophiuroids use this ability to escape predators, similar to how lizards autotomize, or deliberately shed, part of their tails to confuse pursuers.

Locomotion

Brittle stars use their arms for locomotion. They do not, like sea stars, depend on tube feet. Brittle stars move fairly rapidly by wriggling their arms which are highly flexible and enable the animals to make either snake-like or rowing movements. Their movement has some similarities with animals with bilateral symmetry. Orders Forcipulatida Paxillosida Notomyotida Spinulosida Valvatida Velatida Brisingida Starfish redirects here. ...

Trophic levels

Many ophiuroids are 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.

References

http://www.palaeos.com/Invertebrates/Echinoderms/Ophiuroidea/Ophiuroidea.htm