Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

s 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 in length on the largest specimens. The Ophiuroidea contain two large clades,

Ophiurida The Ophiurida are an order of echinoderms within the class Ophiuroidea. It includes the vast majority of living brittle stars. Characteristics Ophiurida have bursae for respiration and excretion, and dorsal and ventral arm shields are present a ...

(brittle stars) and

Euryalida The Euryalida are an order of brittle stars, which includes large species with either branching arms (called "basket stars") or long and curling arms (called "snake stars"). Characteristics Many of the species in this order have characteristi ...

(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.

Range

The ophiuroids diverged in the

Early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

, about 500 million years ago. 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 A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock o ...

communities, where they hide under rocks and even within other living organisms. A few ophiuroid species can even tolerate

brackish water Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

, an ability otherwise almost unknown among echinoderms. A brittle star's skeleton is made up of embedded ossicles.

Anatomy

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, 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 The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a sma ...

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.

Water-vascular system

The vessels of the

water vascular system The water vascular system is a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration. The system is composed of canals connecting numerous tube feet. Echinoderms m ...

end in

tube feet Tube feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on br ...

. 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

ampulla An ampulla (; ) was, in Ancient Rome, a small round vessel, usually made of glass and with two handles, used for sacred purposes. The word is used of these in archaeology, and of later flasks, often handle-less and much flatter, for holy water or ...

e are absent from the tube feet.

Nervous system

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. 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 the ends of their arms, detecting light and retreating into crevices.

Digestion

The mouth is rimmed with five jaws, and serves as an anus (

egestion Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging fro ...

) as well as a mouth (

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms in ...

). 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 the arms. The stomach wall contains glandular

hepatic The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it is ...

cells. Ophiuroids are generally scavengers or

detritivores Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

. 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 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. In

basket star The Euryalida are an order of brittle stars, which includes large species with either branching arms (called "basket stars") or long and curling arms (called "snake stars"). Characteristics Many of the species in this order have characteristi ...

s, the arms are used to sweep food rhythmically to the mouth. ''Pectinura'' consumes beech pollen in the

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

fjords (since those trees hang over the water). ''Eurylina'' clings to coral branches to browse on the

polyps A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end i ...

Respiration

Gas exchange and excretion occur through cilia-lined sacs called bursae; each opens between 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 Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is c ...

"coelomocytes" collecting waste products in the body cavity and then migrating to the bursae for expulsion from the body.

Musculoskeletal system

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 A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleu ...

. In most species, the joints between the ossicles and superficial plates allow the arm to bend to the side, but cannot bend upwards. However, in the

s, 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 The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

" articulate by means of ball-and-socket joints, and are controlled by muscles. They are essentially fused plates which correspond to the parallel ambulacral plates in sea stars and five

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

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 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 Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish a ...

''. In the

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 Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of musc ...

. Ophiuroida move horizontally, and ''Euryalina'' species move 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 the taxa, separating them. Ophiuroida move 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.

Reproduction

The sexes are separate in most species, though a few are hermaphroditic or protandric. The gonads are located in the disk, and open into pouches between the arms, called genital bursae. Fertilisation is external in most species, with the

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

s 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 Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

, with 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 a few species, the female carries a dwarf male, clinging to it with the mouth.

Fission

Some brittle stars, such as the six-armed members of the family

Ophiactidae Ophiactidae are a family of brittle stars. Genera The following genera are recognised by the World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and compr ...

, 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 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 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 is 89 days, so theoretically, each brittle star can produce 15 new individuals during the course of a year.

Life span

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 The Euryalida are an order of brittle stars, which includes large species with either branching arms (called "basket stars") or long and curling arms (called "snake stars"). Characteristics Many of the species in this order have characteristi ...

, such as '' Gorgonocephalus'', may live much longer.

Regeneration

An '' Ophiothrix fragilis'' brittle star with missing arm segments from Póvoa de Varzim, Portugal Ophiuroids can readily Regeneration (biology), regenerate lost arms or arm segments unless all arms are lost. Ophiuroids use this ability anti-predator adaptation, to escape predators, in 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.

Locomotion

Brittle stars use their arms for locomotion. 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. 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 a change in direction is necessary.

Bioluminescence

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.

Ecology

Brittle stars live in areas from the low-tide level downwards. Six families live at least 2 m deep; 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 ''Ophiothrix fragilis'' is a species of brittle star in the order Ophiurida. It is found around the coasts of western Europe and is known in Britain as the common brittle star. It is also found along the coast of South Africa where it is known ...

''). Deep-water species tend to live in or on the sea floor or adhere to coral, urchins, or

xenophyophores Xenophyophorea is a clade of foraminiferans. Members of this class are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their s ...

. The most widespread species is the long-armed brittle star (''Amphipholis squamata''), a grayish or bluish, strongly luminescent species.

Parasites

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.

Diversity and taxonomy

Between and species of brittle stars are currently known, but the total number of modern species may be over . 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 the sediment leaving only their arms in the stream to capture the plankton). There are also 344 species in the family of

Ophiuridae Ophiuridae are a large family of brittle stars of the suborder Ophiurina. Description The arms are simple and unbranched, projecting from and well-fused to the edge of the disc. These arms move horizontally. The arm spines short and movable. ...

. List of families according to the

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained by scientific specialis ...

, following O'Hara 2017: * subclass Myophiuroidea Matsumoto, 1915 ** infra-class Metophiurida Matsumoto, 1913 *** super-order Euryophiurida O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 **** order

Lamarck, 1816 ***** family

Asteronychidae Asteronychidae is a family of echinoderms belonging to the order Euryalida. Genera: * ''Asteronyx'' Müller & Troschel, 1842 * ''Astrodia'' Verrill, 1899 * ''Astronebris'' Downey, 1967 * ''Lillithaster'' Thuy, Numberger-Thuy & Jagt, 2018 * ''Ophi ...

Ljungman, 1867 ***** family Euryalidae Gray, 1840 ***** family Gorgonocephalidae Ljungman, 1867 **** order

Müller & Troschel, 1840 sensu O'Hara et al., 2017 ***** suborder Ophiomusina O'Hara et al., 2017 ****** family Ophiomusaidae (O'Hara, Stöhr, Hugall, Thuy, Martynov, 2018) ****** family Ophiosphalmidae (O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018) ****** Ophiomusina ''incertae sedis'' ***** suborder

Ophiurina Ophiurina are a suborder of brittle stars containing the majority of living brittle star species. Systematics There is currently no consensus as to the subdivision of the Ophiurina (traditionally, the infraorders have been treated as suborders). ...

Müller & Troschel, 1840 sensu O'Hara et al., 2017 ****** family Astrophiuridae Sladen, 1879 ****** family Ophiopyrgidae Perrier, 1893 ****** family

Müller & Troschel, 1840 ****** Ophiurina ''incertae sedis'' ***** Ophiurida ''incertae sedis'' *** Ophioderma (Charleston, South Carolina, 7 February 1852)

super-order Ophintegrida O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 **** order

Amphilepidida Amphilepidida is an order of echinoderms belonging to the class Ophiuroidea Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to ...

O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ***** suborder

Gnathophiurina The Gnathophiurina are a group of Ophiuroidea mostly treated as suborder (but at first as an order Gnathophiurida, and sometimes as infraorder of OphiurinaSmith, A.B.; Paterson, G.L.J. . Ophiuroid phylogeny and higher taxonomy: morphological, mo ...

Matsumoto, 1915 ****** super-family Amphiuroidea Ljungman, 1867 ******* family Amphiuridae Ljungman, 1867 ******* family Amphilepididae Matsumoto, 1915 ****** super-family Ophiactoidea Ljungman, 1867 ******* family

Matsumoto, 1915 ******* family Ophiopholidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ******* family Ophiothamnidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ******* family

Ophiotrichidae Ophiotrichidae are a family of ophiurid brittle stars within the suborder Gnathophiurina. All have arms with delicate translucent, thorny spines. The arms are flexible in all directions. The jaws contain clusters of well-developed tooth papillae ...

Ljungman, 1867 ***** suborder Ophionereidina O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ****** super-family Ophiolepidoidea Ljungman, 1867 ******* family Hemieuryalidae Verrill, 1899 ******* family

Ophiolepididae Ophiolepididae are a family of brittle stars of the suborder Ophiurina. It includes both deep-sea and shallow-water species. Systematics and phylogeny The fossils of Ophiolepididae date back to the Anisian age of the Middle Triassic In the ge ...

Ljungman, 1867 (restricted) ****** super-family Ophionereidoidea Ljungman, 1867 ******* family Amphilimnidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ******* family

Ophionereididae Ophionereididae are a family of brittle stars. Systematics Ophionereididae has been placed (along with Ophiocomidae) to the Taxonomic rank, superfamily Ophiocomidea and infraorder Chilophiurina or suborder Chilophiurina in different classificati ...

Ljungman, 1867 ***** suborder Ophiopsilina Matsumoto, 1915 ****** super-family Ophiopsiloidea Matsumoto, 1915 ******* family Ophiopsilidae Matsumoto, 1915 **** order

Ophiacanthida Ophiacanthida is an order of echinoderms belonging to the class Ophiuroidea. Families: * Ophiodermatina Ljungman, 1867 ** Ophiodermatidae ** Ophiomyxidae ** Ophiopezidae ** Ophiocomidae Ophiocomidae are a family of brittle stars of the sub ...

O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ***** suborder Ophiacanthina O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ****** family Clarkcomidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ****** family Ophiacanthidae Ljungman, 1867 ****** family Ophiobyrsidae Matsumoto, 1915 ****** family Ophiocamacidae (O'Hara, Stöhr, Hugall, Thuy, Martynov, 2018) ****** family Ophiopteridae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ****** family Ophiotomidae Paterson, 1985 ******family

Ophiojuridae ''Ophiojura'' is a genus of brittle star in its own family, Ophiojuridae. It has only one known species, ''Ophiojura exbodi'', collected by the EXBODI expedition from Banc Durand seamount off New Caledonia in 2011 at a depth of . The prefix 'Op ...

O'Hara, Thuy & Hugall, 2021 ***** suborder Ophiodermatina Ljungman, 1867 ****** super-family Ophiocomoidea Ljungman, 1867 ******* family

Ophiocomidae Ophiocomidae are a family of brittle stars of the suborder Ophiurina. Systematics and phylogeny Ophiocomidae has been placed (along with Ophionereididae) to the superfamily Ophiocomidea and infraorder Order ( la, ordo) is one of the eigh ...

Ljungman, 1867 ****** super-family Ophiodermatoidea Ljungman, 1867 ******* family

Ophiodermatidae Ophiodermatidae are a family of brittle stars in the suborder Ophiurina. Systematics and phylogeny Some fossils date as far back as the Changhsingian age, late in the Permian The Permian ( ) is a geologic period and System (stratigraphy), str ...

Ljungman, 1867 ******* family

Ophiomyxidae Ophiomyxidae is a family of echinoderms belonging to the order Ophiacanthida Ophiacanthida is an order of echinoderms belonging to the class Ophiuroidea. Families: * Ophiodermatina Ljungman, 1867 ** Ophiodermatidae ** Ophiomyxidae ** Ophio ...

Ljungman, 1867 ******* family Ophiopezidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ***** Ophiacanthida ''incertae sedis'' **** order Ophioleucida O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ***** family Ophiernidae O'Hara, Stöhr, Hugall, Thuy & Martynov, 2018 ***** family Ophioleucidae Matsumoto, 1915 **** order

Ophioscolecida Ophioscolecida is an order of echinoderms belonging to the class Ophiuroidea Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to ...

O'Hara, Hugall, Thuy, Stöhr & Martynov, 2017 ***** family

Ophiohelidae Ophiohelidae is a family of echinoderms belonging to the order Ophioscolecida Ophioscolecida is an order of echinoderms belonging to the class Ophiuroidea Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms ...

Perrier, 1893 ***** family Ophioscolecidae Lütken, 1869 * Ophiuroidea ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' Image:Tu - Asteronyx loveni 1.jpg , '' Asteronyx loveni'', an

Image:Asteroschematidae Hawaii 01.jpg, Une Asteroschematidae Image:Squamophis albozosteres holotype - ZooKeys-129-001-g003-A.jpeg, '' Squamophis albozosteres'', an Astrocharidae Image:Basket star (Family Euryalidae).jpg, '' Euryale aspera'', an Euryalidae Image:Basket star ar Star Wall DSC00638.JPG, ''

Astrocladus euryale Astrocladus euryale, the basket star, or gorgon's head is a brittlestar of the family Gorgonocephalidae found in the coastal waters of South Africa from the west coast of the Cape Peninsula to about Algoa Bay. Description The 10 arms branch repe ...

'', a Gorgonocephalidae Image:Ophiomusa acufera (MNHN-IE-2013-10284) 02.jpg, '' Ophiomusa acufera'', an Ophiomusaidae Image:Ophiomusium-lymani.jpg, '' Ophiomusium lymani'', an Ophiosphalmidae Image:Ophiomisidium crosnieri (MNHN-IE-2013-10302) 02.jpg , '' Ophiomisidium crosnieri'', an Astrophiuridae Image:Spinophiura jolliveti.jpg, '' Spinophiura jolliveti'', an Ophiopyrgidae Image:OphiureOphiuraOye-Plage2.jpg, ''

Ophiura ophiura ''Ophiura ophiura'' or the serpent star is a species of brittle star in the order Ophiurida. It is typically found on coastal seabeds around northwestern Europe. Description ''Ophiura ophiura'' has a circular central disc up to 35 mm (1.5 ...

'', an

Image:Amphioplus thrombodes.jpg, '' Amphioplus thrombodes'', an Amphiuridae Image:Tiny in-a-sponge brittle stars (Ophiactis savignyi).jpg, '' Ophiactis savignyi'', an

Image:Ophiocoma pica.jpg, ''

Ophiocoma pica ''Ophiocoma'' is a genus of brittle stars belonging to the family Ophiocomidae. Selected species * ''Ophiocoma aethiops'' (Lütken, 1859) * ''Ophiocoma echinata'' (Lamarck, 1816) * ''Ophiocoma erinaceus'' (Müller & Troschel, 1842) * ''Ophiocom ...

'', an

Image:Ophionereis reticulata 1.jpg, '' Ophionereis reticulata'', an

Image:Sponge Brittle Stars.jpg, ''

Ophiothrix suensonii ''Ophiothrix'' is a large genus of brittle stars (Ophiuroidea) found in oceans worldwide from tropics to Arctic and Antarctic regions. At present a total of 93 Ophiothrix species have been recognized. It is considered as one of the most interesti ...

'', an

Clarkcoma canaliculata.jpg , '' Clarkcoma canaliculata'', an Clarkcomidae Image:Ophiacantha alternata.jpg, '' Ophiacantha alternata'', an Ophiacanthidae Image:Ophiocamax fasciculata.jpg, '' Ophiocamax fasciculata'', an Ophiocamacidae Image:Ophiopteris antipodum.JPG , '' Ophiopteris antipodum'', an Ophiopteridae Image:BEP2 3399l.jpg , '' Ophiocomina nigra'', an Ophiotomidae Image:Ophioderma brevispina.jpg, '' Ophioderma brevispina'', an

Image:Ophioplocus bispinosus.jpg, '' Ophioplocus bispinosa'', an Hemieuryalidae Image:Ophiolepis superba Réunion.jpg, '' Ophiolepis superba'', an

Image:Ophiomyxa australis.jpg, '' Ophiomyxa australis'', an

Image:Ophiure à déterminer 8.jpg , '' Ophiopeza cf. fallax'', an Ophiopezidae Image:Ophiernus adspersus annectens (MNHN-IE-2013-10246) 02.jpg, '' Ophiernus adspersus'', an Ophiernidae Image:Ophioleuce seminudum (MNHN-IE-2013-10292) 02.jpg, '' Ophioleuce seminudum'', an Ophioleucidae Image:Ophiomyces frutectosus (MNHN-IE-2013-10282) 02.jpg, '' Ophiomyces frutectosus'', an

Fossil record

The first known brittle stars date from

. 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 the

Agrio Formation The Agrio Formation is an Early Cretaceous geologic formation that is up to thick and is located in the southern Mendoza Province and northern-central Neuquén Province, in the Neuquén Basin of northwestern Patagonia, Argentina.Weaver, C. E. (1 ...

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The bas ...

in the 2010s no fossil brittle star was known in the Southern Hemisphere, nor was any brittle star of

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

age known.

Human relations

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.

Aquaria

Brittle stars are a moderately popular invertebrate in

fishkeeping Fishkeeping is a popular hobby, practiced by aquarists, concerned with keeping fish in a home aquarium or garden pond. There is also a piscicultural fishkeeping industry, serving as a branch of agriculture. Origins of fishkeeping Fish hav ...

. They can easily thrive in marine tanks; in fact, 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 Live rock is rock from the ocean that has been introduced into a saltwater aquarium. Along with live sand, it confers to the closed marine system multiple benefits desired by the saltwater aquarium hobbyist. The name sometimes leads to misunders ...

. 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.

References

* Andrew B. Smith, Howard B. Fell, Daniel B. Blake, Howard B. Fell, "Ophiuroidea", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.471000 * David L. Pawson, Andrew C. Campbell, David L. Pawson, David L. Pawson, Raymond C. Moore, J. John Sepkoski, Jr., "Echinodermata", in AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/1097-8542.210700 * "brittle star."Encyclopædia Britannica. 2008.

Encyclopædia Britannica 2006 Ultimate Reference Suite DVD An encyclopedia (American English) or encyclopædia (British English) is a reference work or compendium providing summaries of knowledge either general or special to a particular field or discipline. Encyclopedias are divided into articles ...

17 June 2008.
Palaeos: Ophiuroidea
{{Taxonbar, from=Q59256 Ophiuroidea Articles containing video clips Extant Ordovician first appearances