Starfish

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"Sea Star" redirects here. Starfish_sentence_0

For other uses, see SeaStar (disambiguation) and Starfish (disambiguation). Starfish_sentence_1

"Asteroidea" redirects here. Starfish_sentence_2

For the Asteraceae subfamily, see Asteroideae. Starfish_sentence_3

Starfish_table_infobox_0

Starfish

Temporal range: Triassic–Recent PreꞒ O S D C P T J K Pg NStarfish_header_cell_0_0_0

Scientific classification AsteroideaStarfish_header_cell_0_1_0
Kingdom:Starfish_cell_0_2_0 AnimaliaStarfish_cell_0_2_1
Phylum:Starfish_cell_0_3_0 EchinodermataStarfish_cell_0_3_1
Superclass:Starfish_cell_0_4_0 AsterozoaStarfish_cell_0_4_1
Class:Starfish_cell_0_5_0 Asteroidea

Blainville, 1830Starfish_cell_0_5_1

Child taxa and ordersStarfish_header_cell_0_6_0

Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Starfish_sentence_4

Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish_sentence_5

Starfish are also known as Asteroids due to being in the class Asteroidea. Starfish_sentence_6

About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. Starfish_sentence_7

They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface. Starfish_sentence_8

Starfish are marine invertebrates. Starfish_sentence_9

They typically have a central disc and usually five arms, though some species have a larger number of arms. Starfish_sentence_10

The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Starfish_sentence_11

Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish_sentence_12

Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. Starfish_sentence_13

They are opportunistic feeders and are mostly predators on benthic invertebrates. Starfish_sentence_14

Several species have specialized feeding behaviours including eversion of their stomachs and suspension feeding. Starfish_sentence_15

They have complex life cycles and can reproduce both sexually and asexually. Starfish_sentence_16

Most can regenerate damaged parts or lost arms and they can shed arms as a means of defense. Starfish_sentence_17

The Asteroidea occupy several significant ecological roles. Starfish_sentence_18

Starfish, such as the ochre sea star (Pisaster ochraceus) and the reef sea star (Stichaster australis), have become widely known as examples of the keystone species concept in ecology. Starfish_sentence_19

The tropical crown-of-thorns starfish (Acanthaster planci) is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific sea star is considered to be one of the world's 100 worst invasive species. Starfish_sentence_20

The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather sparse, as starfish tend to disintegrate after death. Starfish_sentence_21

Only the ossicles and spines of the animal are likely to be preserved, making remains hard to locate. Starfish_sentence_22

With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture. Starfish_sentence_23

They are sometimes collected as curios, used in design or as logos, and in some cultures, despite possible toxicity, they are eaten. Starfish_sentence_24

Anatomy Starfish_section_0

Most starfish have five arms that radiate from a central disc, but the number varies with the group. Starfish_sentence_25

Some species have six or seven arms and others have 10–15 arms. Starfish_sentence_26

The Antarctic Labidiaster annulatus can have over fifty. Starfish_sentence_27

Body wall Starfish_section_1

The body wall consists of a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and a thin coelomic myoepithelial layer, which provides the longitudinal and circular musculature. Starfish_sentence_28

The dermis contains an endoskeleton of calcium carbonate components known as ossicles. Starfish_sentence_29

These are honeycombed structures composed of microcrystals arranged in a lattice. Starfish_sentence_30

They vary in form, with some bearing external granules, tubercles and spines, but most are tabular plates that fit neatly together in a tessellated manner and form the main covering of the aboral surface. Starfish_sentence_31

Some are specialised structures such as the madreporite (the entrance to the water vascular system), pedicellariae and paxillae. Starfish_sentence_32

Pedicellariae are compound ossicles with forceps-like jaws. Starfish_sentence_33

They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements. Starfish_sentence_34

They often form clusters surrounding spines. Starfish_sentence_35

Paxillae are umbrella-like structures found on starfish that live buried in sediment. Starfish_sentence_36

The edges of adjacent paxillae meet to form a false cuticle with a water cavity beneath in which the madreporite and delicate gill structures are protected. Starfish_sentence_37

All the ossicles, including those projecting externally, are covered by the epidermal layer. Starfish_sentence_38

Several groups of starfish, including Valvatida and Forcipulatida, possess pedicellariae. Starfish_sentence_39

In Forcipulatida, such as Asterias and Pisaster, they occur in pompom-like tufts at the base of each spine, whereas in the Goniasteridae, such as Hippasteria phrygiana, the pedicellariae are scattered over the body surface. Starfish_sentence_40

Some are thought to assist in defence, while others aid in feeding or in the removal of organisms attempting to settle on the starfish's surface. Starfish_sentence_41

Some species like Labidiaster annulatus, Rathbunaster californicus and Novodinia antillensis use their large pedicellariae to capture small fish and crustaceans. Starfish_sentence_42

There may also be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water. Starfish_sentence_43

These serve a respiratory function. Starfish_sentence_44

The structures are supported by collagen fibres set at right angles to each other and arranged in a three-dimensional web with the ossicles and papulae in the . Starfish_sentence_45

This arrangement enables both easy flexion of the arms by the starfish and the rapid onset of stiffness and rigidity required for actions performed under stress. Starfish_sentence_46

Water vascular system Starfish_section_2

The water vascular system of the starfish is a hydraulic system made up of a network of fluid-filled canals and is concerned with locomotion, adhesion, food manipulation and gas exchange. Starfish_sentence_47

Water enters the system through the madreporite, a porous, often conspicuous, sieve-like ossicle on the aboral surface. Starfish_sentence_48

It is linked through a stone canal, often lined with calcareous material, to a ring canal around the mouth opening. Starfish_sentence_49

A set of radial canals leads off this; one radial canal runs along the groove in each arm. Starfish_sentence_50

There are short lateral canals branching off alternately to either side of the radial canal, each ending in an ampulla. Starfish_sentence_51

These bulb-shaped organs are joined to tube feet (podia) on the exterior of the animal by short linking canals that pass through ossicles in the ambulacral groove. Starfish_sentence_52

There are usually two rows of tube feet but in some species, the lateral canals are alternately long and short and there appear to be four rows. Starfish_sentence_53

The interior of the whole canal system is lined with cilia. Starfish_sentence_54

When longitudinal muscles in the ampullae contract, valves in the lateral canals close and water is forced into the tube feet. Starfish_sentence_55

These extend to contact the substrate. Starfish_sentence_56

Although the tube feet resemble suction cups in appearance, the gripping action is a function of adhesive chemicals rather than suction. Starfish_sentence_57

Other chemicals and relaxation of the ampullae allow for release from the substrate. Starfish_sentence_58

The tube feet latch on to surfaces and move in a wave, with one arm section attaching to the surface as another releases. Starfish_sentence_59

Some starfish turn up the tips of their arms while moving which gives maximum exposure of the sensory tube feet and the eyespot to external stimuli. Starfish_sentence_60

Having descended from bilateral organisms, starfish may move in a bilateral fashion, particularly when hunting or in danger. Starfish_sentence_61

When crawling, certain arms act as the leading arms, while others trail behind. Starfish_sentence_62

Most starfish cannot move quickly, a typical speed being that of the leather star (Dermasterias imbricata), which can manage just 15 cm (6 in) in a minute. Starfish_sentence_63

Some burrowing species from the genera Astropecten and Luidia have points rather than suckers on their long tube feet and are capable of much more rapid motion, "gliding" across the ocean floor. Starfish_sentence_64

The sand star (Luidia foliolata) can travel at a speed of 2.8 m (9 ft 2 in) per minute. Starfish_sentence_65

When a starfish finds itself upside down, two adjacent arms are bent backwards to provide support, the opposite arm is used to stamp the ground while the two remaining arms are raised on either side; finally the stamping arm is released as the starfish turns itself over and recovers its normal stance. Starfish_sentence_66

Apart from their function in locomotion, the tube feet act as accessory gills. Starfish_sentence_67

The water vascular system serves to transport oxygen from, and carbon dioxide to, the tube feet and also nutrients from the gut to the muscles involved in locomotion. Starfish_sentence_68

Fluid movement is bidirectional and initiated by cilia. Starfish_sentence_69

Gas exchange also takes place through other gills known as papulae, which are thin-walled bulges on the aboral surface of the disc and arms. Starfish_sentence_70

Oxygen is transferred from these to the coelomic fluid, which acts as the transport medium for gasses. Starfish_sentence_71

Oxygen dissolved in the water is distributed through the body mainly by the fluid in the main body cavity; the circulatory system may also play a minor role. Starfish_sentence_72

Digestive system and excretion Starfish_section_3

The gut of a starfish occupies most of the disc and extends into the arms. Starfish_sentence_73

The mouth is located in the centre of the oral surface, where it is surrounded by a tough membrane and closed with a sphincter. Starfish_sentence_74

The mouth opens through a short oesophagus into a stomach divided by a constriction into a larger, cardiac portion and a smaller pyloric portion. Starfish_sentence_75

The cardiac stomach is glandular and pouched, and is supported by ligaments attached to ossicles in the arms so it can be pulled back into position after it has been everted. Starfish_sentence_76

The pyloric stomach has two extensions into each arm: the pyloric caeca. Starfish_sentence_77

These are elongated, branched hollow tubes that are lined by a series of glands, which secrete digestive enzymes and absorb nutrients from the food. Starfish_sentence_78

A short intestine and rectum run from the pyloric stomach to open at a small anus at the apex of the aboral surface of the disc. Starfish_sentence_79

Primitive starfish, such as Astropecten and Luidia, swallow their prey whole, and start to digest it in their cardiac stomachs. Starfish_sentence_80

Shell valves and other inedible materials are ejected through their mouths. Starfish_sentence_81

The semi-digested fluid is passed into their pyloric stomachs and caeca where digestion continues and absorption ensues. Starfish_sentence_82

In more advanced species of starfish, the cardiac stomach can be everted from the organism's body to engulf and digest food. Starfish_sentence_83

When the prey is a clam or other bivalve, the starfish pulls with its tube feet to separate the two valves slightly, and inserts a small section of its stomach, which releases enzymes to digest the prey. Starfish_sentence_84

The stomach and the partially digested prey are later retracted into the disc. Starfish_sentence_85

Here the food is passed on to the pyloric stomach, which always remains inside the disc. Starfish_sentence_86

The retraction and contraction of the cardiac stomach is activated by a neuropeptide known as NGFFYamide. Starfish_sentence_87

Because of this ability to digest food outside the body, starfish can hunt prey much larger than their mouths. Starfish_sentence_88

Their diets include clams and oysters, arthropods, small fish and gastropod molluscs. Starfish_sentence_89

Some starfish are not pure carnivores, supplementing their diets with algae or organic detritus. Starfish_sentence_90

Some of these species are grazers, but others trap food particles from the water in sticky mucus strands that are swept towards the mouth along ciliated grooves. Starfish_sentence_91

The main nitrogenous waste product is ammonia. Starfish_sentence_92

Starfish have no distinct excretory organs; waste ammonia is removed by diffusion through the tube feet and papulae. Starfish_sentence_93

The body fluid contains phagocytic cells called coelomocytes, which are also found within the hemal and water vascular systems. Starfish_sentence_94

These cells engulf waste material, and eventually migrate to the tips of the papulae, where a portion of body wall is nipped off and ejected into the surrounding water. Starfish_sentence_95

Some waste may also be excreted by the pyloric glands and voided with the faeces. Starfish_sentence_96

Starfish do not appear to have any mechanisms for osmoregulation, and keep their body fluids at the same salt concentration as the surrounding water. Starfish_sentence_97

Although some species can tolerate relatively low salinity, the lack of an osmoregulation system probably explains why starfish are not found in fresh water or even in many estuarine environments. Starfish_sentence_98

Sensory and nervous systems Starfish_section_4

Although starfish do not have many well-defined sense organs, they are sensitive to touch, light, temperature, orientation and the status of the water around them. Starfish_sentence_99

The tube feet, spines and pedicellariae are sensitive to touch. Starfish_sentence_100

The tube feet, especially those at the tips of the rays, are also sensitive to chemicals, enabling the starfish to detect odour sources such as food. Starfish_sentence_101

There are eyespots at the ends of the arms, each one made of 80–200 simple ocelli. Starfish_sentence_102

These are composed of pigmented epithelial cells that respond to light and are covered by a thick, transparent cuticle that both protects the ocelli and acts to focus light. Starfish_sentence_103

Many starfish also possess individual photoreceptor cells in other parts of their bodies and respond to light even when their eyespots are covered. Starfish_sentence_104

Whether they advance or retreat depends on the species. Starfish_sentence_105

While a starfish lacks a centralized brain, it has a complex nervous system with a nerve ring around the mouth and a radial nerve running along the ambulacral region of each arm parallel to the radial canal. Starfish_sentence_106

The peripheral nerve system consists of two nerve nets: a sensory system in the epidermis and a motor system in the lining of the coelomic cavity. Starfish_sentence_107

Neurons passing through the dermis connect the two. Starfish_sentence_108

The ring nerves and radial nerves have sensory and motor components and coordinate the starfish's balance and directional systems. Starfish_sentence_109

The sensory component receives input from the sensory organs while the motor nerves control the tube feet and musculature. Starfish_sentence_110

The starfish does not have the capacity to plan its actions. Starfish_sentence_111

If one arm detects an attractive odour, it becomes dominant and temporarily over-rides the other arms to initiate movement towards the prey. Starfish_sentence_112

The mechanism for this is not fully understood. Starfish_sentence_113

Circulatory system Starfish_section_5

The body cavity contains the circulatory or haemal system. Starfish_sentence_114

The vessels form three rings: one around the mouth (the hyponeural haemal ring), another around the digestive system (the gastric ring) and the third near the aboral surface (the genital ring). Starfish_sentence_115

The heart beats about six times a minute and is at the apex of a vertical channel (the axial vessel) that connects the three rings. Starfish_sentence_116

At the base of each arm are paired gonads; a lateral vessel extends from the genital ring past the gonads to the tip of the arm. Starfish_sentence_117

This vessel has a blind end and there is no continuous circulation of the fluid within it. Starfish_sentence_118

This liquid does not contain a pigment and has little or no respiratory function but is probably used to transport nutrients around the body. Starfish_sentence_119

Secondary metabolites Starfish_section_6

Starfish produce a large number of secondary metabolites in the form of lipids, including steroidal derivatives of cholesterol, and fatty acid amides of sphingosine. Starfish_sentence_120

The steroids are mostly saponins, known as asterosaponins, and their sulphated derivatives. Starfish_sentence_121

They vary between species and are typically formed from up to six sugar molecules (usually glucose and galactose) connected by up to three glycosidic chains. Starfish_sentence_122

Long-chain fatty acid amides of sphingosine occur frequently and some of them have known pharmacological activity. Starfish_sentence_123

Various ceramides are also known from starfish and a small number of alkaloids have also been identified. Starfish_sentence_124

The functions of these chemicals in the starfish have not been fully investigated but most have roles in defence and communication. Starfish_sentence_125

Some are feeding deterrents used by the starfish to discourage predation. Starfish_sentence_126

Others are and supplement the pedicellariae to prevent other organisms from settling on the starfish's aboral surface. Starfish_sentence_127

Some are alarm pheromones and escape-eliciting chemicals, the release of which trigger responses in conspecific starfish but often produce escape responses in potential prey. Starfish_sentence_128

Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide. Starfish_sentence_129

Life cycle Starfish_section_7

Sexual reproduction Starfish_section_8

Most species of starfish are gonochorous, there being separate male and female individuals. Starfish_sentence_130

These are usually not distinguishable externally as the gonads cannot be seen, but their sex is apparent when they spawn. Starfish_sentence_131

Some species are simultaneous hermaphrodites, producing eggs and sperm at the same time and in a few of these, the same gonad, called an ovotestis, produces both eggs and sperm. Starfish_sentence_132

Other starfish are sequential hermaphrodites. Starfish_sentence_133

Protandrous individuals of species like Asterina gibbosa start life as males before changing sex into females as they grow older. Starfish_sentence_134

In some species such as Nepanthia belcheri, a large female can split in half and the resulting offspring are males. Starfish_sentence_135

When these grow large enough they change back into females. Starfish_sentence_136

Each starfish arm contains two gonads that release gametes through openings called gonoducts, located on the central disc between the arms. Starfish_sentence_137

Fertilization is generally external but in a few species, internal fertilization takes place. Starfish_sentence_138

In most species, the buoyant eggs and sperm are simply released into the water (free spawning) and the resulting embryos and larvae live as part of the plankton. Starfish_sentence_139

In others, the eggs may be stuck to the undersides of rocks. Starfish_sentence_140

In certain species of starfish, the females brood their eggs – either by simply enveloping them or by holding them in specialised structures. Starfish_sentence_141

Brooding may be done in pockets on the starfish's aboral surface, inside the pyloric stomach (Leptasterias tenera) or even in the interior of the gonads themselves. Starfish_sentence_142

Those starfish that brood their eggs by "sitting" on them usually assume a humped posture with their discs raised off the substrate. Starfish_sentence_143

Pteraster militaris broods a few of its young and disperses the remaining eggs, that are too numerous to fit into its pouch. Starfish_sentence_144

In these brooding species, the eggs are relatively large, and supplied with yolk, and they generally develop directly into miniature starfish without an intervening larval stage. Starfish_sentence_145

The developing young are called lecithotrophic because they obtain their nutrition from the yolk as opposed to "planktotrophic" larvae that feed in the water column. Starfish_sentence_146

In Parvulastra parvivipara, an brooder, the young starfish obtain nutrients by eating other eggs and embryos in the brood pouch. Starfish_sentence_147

Brooding is especially common in polar and deep-sea species that live in environments unfavourable for larval development and in smaller species that produce just a few eggs. Starfish_sentence_148

In the tropics, a plentiful supply of phytoplankton is continuously available for starfish larvae to feed on. Starfish_sentence_149

Spawning takes place at any time of year, each species having its own characteristic breeding season. Starfish_sentence_150

In temperate regions, the spring and summer brings an increase in food supplies. Starfish_sentence_151

The first individual of a species to spawn may release a pheromone that serves to attract other starfish to aggregate and to release their gametes synchronously. Starfish_sentence_152

In other species, a male and female may come together and form a pair. Starfish_sentence_153

This behaviour is called pseudocopulation and the male climbs on top, placing his arms between those of the female. Starfish_sentence_154

When she releases eggs into the water, he is induced to spawn. Starfish_sentence_155

Starfish may use environmental signals to coordinate the time of spawning (day length to indicate the correct time of the year, dawn or dusk to indicate the correct time of day), and chemical signals to indicate their readiness to breed. Starfish_sentence_156

In some species, mature females produce chemicals to attract sperm in the sea water. Starfish_sentence_157

Larval development Starfish_section_9

Most starfish embryos hatch at the blastula stage. Starfish_sentence_158

The original ball of cells develops a lateral pouch, the archenteron. Starfish_sentence_159

The entrance to this is known as the blastopore and it will later develop into the anus—together with chordates, echinoderms are deuterostomes, meaning the second (deutero) invagination becomes the mouth (stome); members of all other phyla are protostomes, and their first invagination becomes the mouth. Starfish_sentence_160

Another invagination of the surface will fuse with the tip of the archenteron as the mouth while the interior section will become the gut. Starfish_sentence_161

At the same time, a band of cilia develops on the exterior. Starfish_sentence_162

This enlarges and extends around the surface and eventually onto two developing arm-like outgrowths. Starfish_sentence_163

At this stage the larva is known as a bipinnaria. Starfish_sentence_164

The cilia are used for locomotion and feeding, their rhythmic beat wafting phytoplankton towards the mouth. Starfish_sentence_165

The next stage in development is a brachiolaria larva and involves the growth of three short, additional arms. Starfish_sentence_166

These are at the anterior end, surround a sucker and have adhesive cells at their tips. Starfish_sentence_167

Both bipinnaria and brachiolaria larvae are bilaterally symmetrical. Starfish_sentence_168

When fully developed, the brachiolaria settles on the seabed and attaches itself with a short stalk formed from the ventral arms and sucker. Starfish_sentence_169

Metamorphosis now takes place with a radical rearrangement of tissues. Starfish_sentence_170

The left side of the larval body becomes the oral surface of the juvenile and the right side the aboral surface. Starfish_sentence_171

Part of the gut is retained, but the mouth and anus move to new positions. Starfish_sentence_172

Some of the body cavities degenerate but others become the water vascular system and the visceral coelom. Starfish_sentence_173

The starfish is now pentaradially symmetrical. Starfish_sentence_174

It casts off its stalk and becomes a free-living juvenile starfish about 1 mm (0.04 in) in diameter. Starfish_sentence_175

Starfish of the order Paxillosida have no brachiolaria stage, with the bipinnaria larvae settling on the seabed and developing directly into juveniles. Starfish_sentence_176

Asexual reproduction Starfish_section_10

Main article: Asexual reproduction in starfish Starfish_sentence_177

Some species of starfish are able to reproduce asexually as adults either by fission of their central discs or by autotomy of one or more of their arms. Starfish_sentence_178

Which of these processes occurs depends on the genus. Starfish_sentence_179

Among starfish that are able to regenerate their whole body from a single arm, some can do so even from fragments just 1 cm (0.4 in) long. Starfish_sentence_180

Single arms that regenerate a whole individual are called comet forms. Starfish_sentence_181

The division of the starfish, either across its disc or at the base of the arm, is usually accompanied by a weakness in the structure that provides a fracture zone. Starfish_sentence_182

The larvae of several species of starfish can reproduce asexually before they reach maturity. Starfish_sentence_183

They do this by autotomising some parts of their bodies or by budding. Starfish_sentence_184

When such a larva senses that food is plentiful, it takes the path of asexual reproduction rather than normal development. Starfish_sentence_185

Though this costs it time and energy and delays maturity, it allows a single larva to give rise to multiple adults when the conditions are appropriate. Starfish_sentence_186

Regeneration Starfish_section_11

Main article: Starfish regeneration Starfish_sentence_187

Some species of starfish have the ability to regenerate lost arms and can regrow an entire new limb given time. Starfish_sentence_188

A few can regrow a complete new disc from a single arm, while others need at least part of the central disc to be attached to the detached part. Starfish_sentence_189

Regrowth can take several months or years, and starfish are vulnerable to infections during the early stages after the loss of an arm. Starfish_sentence_190

A separated limb lives off stored nutrients until it regrows a disc and mouth and is able to feed again. Starfish_sentence_191

Other than fragmentation carried out for the purpose of reproduction, the division of the body may happen inadvertently due to part being detached by a predator, or part may be actively shed by the starfish in an escape response. Starfish_sentence_192

The loss of parts of the body is achieved by the rapid softening of a special type of connective tissue in response to nervous signals. Starfish_sentence_193

This type of tissue is called catch connective tissue and is found in most echinoderms. Starfish_sentence_194

An autotomy-promoting factor has been identified which, when injected into another starfish, causes rapid shedding of arms. Starfish_sentence_195

Lifespan Starfish_section_12

The lifespan of a starfish varies considerably between species, generally being longer in larger forms and in those with planktonic larvae. Starfish_sentence_196

For example, Leptasterias hexactis broods a small number of large-yolked eggs. Starfish_sentence_197

It has an adult weight of 20 g (0.7 oz), reaches sexual maturity in two years and lives for about ten years. Starfish_sentence_198

Pisaster ochraceus releases a large number of eggs into the sea each year and has an adult weight of up to 800 g (28 oz). Starfish_sentence_199

It reaches maturity in five years and has a maximum recorded lifespan of 34 years. Starfish_sentence_200

Ecology Starfish_section_13

Distribution and habitat Starfish_section_14

Echinoderms, including starfish, maintain a delicate internal electrolyte balance that is in equilibrium with sea water, making it impossible for them to live in a freshwater habitat. Starfish_sentence_201

Starfish species inhabit all of the world's oceans. Starfish_sentence_202

Habitats range from tropical coral reefs, rocky shores, tidal pools, mud, and sand to kelp forests, seagrass meadows and the deep-sea floor down to at least 6,000 m (20,000 ft). Starfish_sentence_203

The greatest diversity of species occurs in coastal areas. Starfish_sentence_204

Diet Starfish_section_15

Most species are generalist predators, eating microalgae, sponges, bivalves, snails and other small animals. Starfish_sentence_205

The crown-of-thorns starfish consumes coral polyps, while other species are detritivores, feeding on decomposing organic material and faecal matter. Starfish_sentence_206

A few are suspension feeders, gathering in phytoplankton; Henricia and Echinaster often occur in association with sponges, benefiting from the water current they produce. Starfish_sentence_207

Various species have been shown to be able to absorb organic nutrients from the surrounding water, and this may form a significant portion of their diet. Starfish_sentence_208

The processes of feeding and capture may be aided by special parts; Pisaster brevispinus, the short-spined pisaster from the West Coast of America, can use a set of specialized tube feet to dig itself deep into the soft substrate to extract prey (usually clams). Starfish_sentence_209

Grasping the shellfish, the starfish slowly pries open the prey's shell by wearing out its adductor muscle, and then inserts its everted stomach into the crack to digest the soft tissues. Starfish_sentence_210

The gap between the valves need only be a fraction of a millimetre wide for the stomach to gain entry. Starfish_sentence_211

Ecological impact Starfish_section_16

Starfish are keystone species in their respective marine communities. Starfish_sentence_212

Their relatively large sizes, diverse diets and ability to adapt to different environments makes them ecologically important. Starfish_sentence_213

The term "keystone species" was in fact first used by Robert Paine in 1966 to describe a starfish, Pisaster ochraceus. Starfish_sentence_214

When studying the low intertidal coasts of Washington state, Paine found that predation by P. ochraceus was a major factor in the diversity of species. Starfish_sentence_215

Experimental removals of this top predator from a stretch of shoreline resulted in lower species diversity and the eventual domination of Mytilus mussels, which were able to outcompete other organisms for space and resources. Starfish_sentence_216

Similar results were found in a 1971 study of Stichaster australis on the intertidal coast of the South Island of New Zealand. Starfish_sentence_217

S. australis was found to have removed most of a batch of transplanted mussels within two or three months of their placement, while in an area from which S. australis had been removed, the mussels increased in number dramatically, overwhelming the area and threatening biodiversity. Starfish_sentence_218

The feeding activity of the omnivorous starfish Oreaster reticulatus on sandy and seagrass bottoms in the Virgin Islands appears to regulate the diversity, distribution and abundance of microorganisms. Starfish_sentence_219

These starfish engulf piles of sediment removing the surface films and algae adhering to the particles. Starfish_sentence_220

Organisms that dislike this disturbance are replaced by others better able to rapidly recolonise "clean" sediment. Starfish_sentence_221

In addition, foraging by these migratory starfish creates diverse patches of organic matter, which may play a role in the distribution and abundance of organisms such as fish, crabs and sea urchins that feed on the sediment. Starfish_sentence_222

Starfish sometimes have negative effects on ecosystems. Starfish_sentence_223

Outbreaks of crown-of-thorns starfish have caused damage to coral reefs in Northeast Australia and French Polynesia. Starfish_sentence_224

A study in Polynesia found that coral cover declined drastically with the arrival of migratory starfish in 2006, dropping from 50% to under 5% in three years. Starfish_sentence_225

This had a cascading effect on the whole benthic community and reef-feeding fish. Starfish_sentence_226

Asterias amurensis is one of a few echinoderm invasive species. Starfish_sentence_227

Its larvae likely arrived in Tasmania from central Japan via water discharged from ships in the 1980s. Starfish_sentence_228

The species has since grown in numbers to the point where they threaten commercially important bivalve populations. Starfish_sentence_229

As such, they are considered pests, and are on the Invasive Species Specialist Group's list of the world's 100 worst invasive species. Starfish_sentence_230

Threats Starfish_section_17

Starfish may be preyed on by conspecifics, sea anemones, other starfish species, tritons, crabs, fish, gulls and sea otters. Starfish_sentence_231

Their first lines of defence are the saponins present in their body walls, which have unpleasant flavours. Starfish_sentence_232

Some starfish such as Astropecten polyacanthus also include powerful toxins such as tetrodotoxin among their chemical armoury, and the slime star can ooze out large quantities of repellent mucus. Starfish_sentence_233

They also have body armour in the form of hard plates and spines. Starfish_sentence_234

The crown-of-thorns starfish is particularly unattractive to potential predators, being heavily defended by sharp spines, laced with toxins and sometimes with bright warning colours. Starfish_sentence_235

Other species protect their vulnerable tube feet and arm tips by lining their ambulacral grooves with spines and heavily plating their extremities. Starfish_sentence_236

Several species sometimes suffer from a wasting condition caused by bacteria in the genus Vibrio; however, a more widespread wasting disease, causing mass mortalities among starfish, appears sporadically. Starfish_sentence_237

A paper published in November 2014 revealed the most likely cause of this disease to be a densovirus the authors named sea star-associated densovirus (SSaDV). Starfish_sentence_238

The protozoan Orchitophrya stellarum is known to infect the gonads of starfish and damage tissue. Starfish_sentence_239

Starfish are vulnerable to high temperatures. Starfish_sentence_240

Experiments have shown that the feeding and growth rates of P. ochraceus reduce greatly when their body temperatures rise above 23 °C (73 °F) and that they die when their temperature rises to 30 °C (86 °F). Starfish_sentence_241

This species has a unique ability to absorb seawater to keep itself cool when it is exposed to sunlight by a receding tide. Starfish_sentence_242

It also appears to rely on its arms to absorb heat, so as to protect the central disc and vital organs like the stomach. Starfish_sentence_243

Starfish and other echinoderms are sensitive to marine pollution. Starfish_sentence_244

The common starfish is considered to be a bioindicator for marine ecosystems. Starfish_sentence_245

A 2009 study found that P. ochraceus is unlikely to be affected by ocean acidification as severely as other marine animals with calcareous skeletons. Starfish_sentence_246

In other groups, structures made of calcium carbonate are vulnerable to dissolution when the pH is lowered. Starfish_sentence_247

Researchers found that when P. ochraceus were exposed to 21 °C (70 °F) and 770 ppm carbon dioxide (beyond rises expected in the next century), they were relatively unaffected. Starfish_sentence_248

Their survival is likely due to the nodular nature of their skeletons, which are able to compensate for a shortage of carbonate by growing more fleshy tissue. Starfish_sentence_249

Evolution Starfish_section_18

Fossil record Starfish_section_19

Echinoderms first appeared in the fossil record in the Cambrian. Starfish_sentence_250

The first known asterozoans were the Somasteroidea, which exhibit characteristics of both groups. Starfish_sentence_251

Starfish are infrequently found as fossils, possibly because their hard skeletal components separate as the animal decays. Starfish_sentence_252

Despite this, there are a few places where accumulations of complete skeletal structures occur, fossilized in place in Lagerstätten – so-called "starfish beds". Starfish_sentence_253

By the late Paleozoic, the crinoids and blastoids were the predominant echinoderms, and some limestones from this period are made almost entirely from fragments from these groups. Starfish_sentence_254

In the two major extinction events that occurred during the late Devonian and late Permian, the blastoids were wiped out and only a few species of crinoids survived. Starfish_sentence_255

Many starfish species also became extinct in these events, but afterwards the surviving few species diversified rapidly within about sixty million years during the Early Jurassic and the beginning of the Middle Jurassic. Starfish_sentence_256

A 2012 study found that speciation in starfish can occur rapidly. Starfish_sentence_257

During the last 6,000 years, divergence in the larval development of Cryptasterina hystera and Cryptasterina pentagona has taken place, the former adopting internal fertilization and brooding and the latter remaining a broadcast spawner. Starfish_sentence_258

Diversity Starfish_section_20

See also: List of echinodermata orders Starfish_sentence_259

The scientific name Asteroidea was given to starfish by the French zoologist de Blainville in 1830. Starfish_sentence_260

It is derived from the Greek aster, ἀστήρ (a star) and the Greek eidos, εἶδος (form, likeness, appearance). Starfish_sentence_261

The class Asteroidea belongs to the phylum Echinodermata. Starfish_sentence_262

As well as the starfish, the echinoderms include sea urchins, sand dollars, brittle and basket stars, sea cucumbers and crinoids. Starfish_sentence_263

The larvae of echinoderms have bilateral symmetry, but during metamorphosis this is replaced with radial symmetry, typically pentameric. Starfish_sentence_264

Adult echinoderms are characterized by having a water vascular system with external tube feet and a calcareous endoskeleton consisting of ossicles connected by a mesh of collagen fibres. Starfish_sentence_265

Starfish are included in the subphylum Asterozoa, the characteristics of which include a flattened, star-shaped body as adults consisting of a central disc and multiple radiating arms. Starfish_sentence_266

The subphylum includes the two classes of Asteroidea, the starfish, and Ophiuroidea, the brittle stars and basket stars. Starfish_sentence_267

Asteroids have broad-based arms with skeletal support provided by calcareous plates in the body wall while ophiuroids have clearly demarcated slender arms strengthened by paired fused ossicles forming jointed "vertebrae". Starfish_sentence_268

The starfish are a large and diverse class with about 1,500 living species. Starfish_sentence_269

There are seven extant orders, Brisingida, Forcipulatida, Notomyotida, Paxillosida, Spinulosida, Valvatida and Velatida and two extinct ones, Calliasterellidae and Trichasteropsida. Starfish_sentence_270

Living asteroids, the Neoasteroidea, are morphologically distinct from their forerunners in the Paleozoic. Starfish_sentence_271

The taxonomy of the group is relatively stable but there is ongoing debate about the status of the Paxillosida, and the deep-water sea daisies, though clearly Asteroidea and currently included in Velatida, do not fit easily in any accepted lineage. Starfish_sentence_272

Phylogenetic data suggests that they may be a sister group, the Concentricycloidea, to the Neoasteroidea, or that the Velatida themselves may be a sister group. Starfish_sentence_273

Living groups Starfish_section_21

Starfish_description_list_0

  • Brisingida (2 families, 17 genera, 111 species): Species in this order have a small, inflexible disc and 6–20 long, thin arms, which they use for suspension feeding. They have a single series of marginal plates, a fused ring of disc plates, a reduced number of aboral plates, crossed pedicellariae, and several series of long spines on the arms. They live almost exclusively in deep-sea habitats, although a few live in shallow waters in the Antarctic. In some species, the tube feet have rounded tips and lack suckers.Starfish_item_0_0

Starfish_description_list_1

  • Forcipulatida (6 families, 63 genera, 269 species): Species in this order have distinctive pedicellariae, consisting of a short stalk with three skeletal ossicles. They tend to have robust bodies and have tube feet with flat-tipped suckers usually arranged in four rows. The order includes well-known species from temperate regions, including the common starfish of North Atlantic coasts and rock pools, as well as cold-water and abyssal species.Starfish_item_1_1
  • Notomyotida (1 family, 8 genera, 75 species): These starfish are deep-sea dwelling and have particularly flexible arms. The inner dorso-lateral surfaces of the arms contain characteristic longitudinal muscle bands. In some species, the tube feet lack suckers.Starfish_item_1_2

Starfish_description_list_2

  • Paxillosida (7 families, 48 genera, 372 species): This is a primitive order and members do not extrude their stomach when feeding, lack an anus and have no suckers on their tube feet. Papulae are plentiful on their aboral surface and they possess marginal plates and paxillae. They mostly inhabit soft-bottomed areas of sand or mud. There is no brachiolaria stage in their larval development. The comb starfish (Astropecten polyacanthus) is a member of this order.Starfish_item_2_3

Starfish_description_list_3

  • Spinulosida (1 family, 8 genera, 121 species): Most species in this order lack pedicellariae and all have a delicate skeletal arrangement with small or no marginal plates on the disc and arms. They have numerous groups of short spines on the aboral surface. This group includes the red starfish Echinaster sepositus.Starfish_item_3_4
  • Valvatida (16 families, 172 genera, 695 species): Most species in this order have five arms and two rows of tube feet with suckers. There are conspicuous marginal plates on the arms and disc. Some species have paxillae and in some, the main pedicellariae are clamp-like and recessed into the skeletal plates. This group includes the cushion stars, the leather star and the sea daisies.Starfish_item_3_5
  • Velatida (4 families, 16 genera, 138 species): This order of starfish consists mostly of deep-sea and other cold-water starfish often with a global distribution. The shape is pentagonal or star-shaped with five to fifteen arms. They mostly have poorly developed skeletons with papulae widely distributed on the aboral surface and often spiny pedicellariae. This group includes the slime star.Starfish_item_3_6

Extinct groups Starfish_section_22

Extinct groups within the Asteroidea include: Starfish_sentence_274

Starfish_unordered_list_4

Phylogeny Starfish_section_23

External Starfish_section_24

Starfish are deuterostome animals, like the chordates. Starfish_sentence_275

A 2014 analysis of 219 genes from all classes of echinoderms gives the following phylogenetic tree. Starfish_sentence_276

The times at which the clades diverged is shown under the labels in millions of years ago (mya). Starfish_sentence_277

Internal Starfish_section_25

The phylogeny of the Asteroidea has been difficult to resolve, with visible (morphological) features proving inadequate, and the question of whether traditional taxa are clades in doubt. Starfish_sentence_278

The phylogeny proposed by Gale in 1987 is: Starfish_sentence_279

The phylogeny proposed by Blake in 1987 is: Starfish_sentence_280

Later work making use of molecular evidence, with or without the use of morphological evidence, had by 2000 failed to resolve the argument. Starfish_sentence_281

In 2011, on further molecular evidence, Janies and colleagues noted that the phylogeny of the echinoderms "has proven difficult", and that "the overall phylogeny of extant echinoderms remains sensitive to the choice of analytical methods". Starfish_sentence_282

They presented a phylogenetic tree for the living Asteroidea only; using the traditional names of starfish orders where possible, and indicating "part of" otherwise, the phylogeny is shown below. Starfish_sentence_283

The Solasteridae are split from the Velatida, and the old Spinulosida is broken up. Starfish_sentence_284

Human relations Starfish_section_26

In research Starfish_section_27

Starfish are deuterostomes, closely related, together with all other echinoderms, to chordates, and are used in reproductive and developmental studies. Starfish_sentence_285

Female starfish produce large numbers of oocytes that are easily isolated; these can be stored in a pre-meiosis phase and stimulated to complete division by the use of 1-methyladenine. Starfish_sentence_286

Starfish oocytes are well suited for this research as they are large and easy to handle, transparent, simple to maintain in sea water at room temperature, and they develop rapidly. Starfish_sentence_287

Asterina pectinifera, used as a model organism for this purpose, is resilient and easy to breed and maintain in the laboratory. Starfish_sentence_288

Another area of research is the ability of starfish to regenerate lost body parts. Starfish_sentence_289

The stem cells of adult humans are incapable of much differentiation and understanding the regrowth, repair and cloning processes in starfish may have implications for human medicine. Starfish_sentence_290

Starfish also have an unusual ability to expel foreign objects from their bodies, which makes them difficult to tag for research tracking purposes. Starfish_sentence_291

In legend and culture Starfish_section_28

An aboriginal Australian fable retold by the Welsh school headmaster William Jenkyn Thomas (1870–1959) tells how some animals needed a canoe to cross the ocean. Starfish_sentence_292

Whale had one but refused to lend it, so Starfish kept him busy, telling him stories and grooming him to remove parasites, while the others stole the canoe. Starfish_sentence_293

When Whale realized the trick he beat Starfish ragged, which is how Starfish still is today. Starfish_sentence_294

In 1900, the scholar Edward Tregear documented The Creation Song, which he describes as "an ancient prayer for the dedication of a high chief" of Hawaii. Starfish_sentence_295

Among the "uncreated gods" described early in the song are the male Kumilipo ("Creation") and the female Poele, both born in the night, a coral insect, the earthworm, and the starfish. Starfish_sentence_296

Georg Eberhard Rumpf's 1705 The Ambonese Curiosity Cabinet describes the tropical varieties of Stella Marina or Bintang Laut, "Sea Star", in Latin and Malay respectively, known in the waters around Ambon. Starfish_sentence_297

He writes that the Histoire des Antilles reports that when the sea stars "see thunder storms approaching, [they] grab hold of many small stones with their little legs, looking to ... hold themselves down as if with anchors". Starfish_sentence_298

Starfish is the title of novels by Peter Watts and Jennie Orbell, and in 2012, Alice Addison wrote a non-fiction book titled "Starfish - A year in the life of bereavement and depression". Starfish_sentence_299

The Starfish and the Spider is a 2006 business management book by Ori Brafman and Rod Beckstrom; its title alludes to the ability of the starfish to regenerate itself because of its decentralized nervous system, and the book suggests ways that a decentralized organisation may flourish. Starfish_sentence_300

In his 2002 book The Divine Mystery Fort, Sri Sai Kaleshwar Swami wrote, "An eighth type of supernatural power object is a starfish. Starfish_sentence_301

Sometimes at the full moon time, when the moon is really dazzling and hitting on the ocean, a starfish jumps out of the water and falls down. Starfish_sentence_302

If you can get that you can suck unbelievable cosmic energy. Starfish_sentence_303

You can use it as your own power object. Starfish_sentence_304

It has to be only on the full moon day when it comes up." Starfish_sentence_305

In the Nickelodeon animated television series SpongeBob SquarePants, the character's best friend is a dim-witted starfish, Patrick Star. Starfish_sentence_306

As food Starfish_section_29

Starfish are widespread in the oceans, but are only occasionally used as food. Starfish_sentence_307

There may be good reason for this: the bodies of numerous species are dominated by bony ossicles, and the body wall of many species contains saponins, which have an unpleasant taste, and others contain tetrodotoxins which are poisonous. Starfish_sentence_308

Some species that prey on bivalve molluscs can transmit paralytic shellfish poisoning. Starfish_sentence_309

Georg Eberhard Rumpf found few starfish being used for food in the Indonesian archipelago, other than as bait in fish traps, but on the island of "Huamobel" sic the people cut them up, squeeze out the "black blood" and cook them with sour tamarind leaves; after resting the pieces for a day or two, they remove the outer skin and cook them in coconut milk. Starfish_sentence_310

Starfish are sometimes eaten in China, Japan and in Micronesia. Starfish_sentence_311

As collectables Starfish_section_30

Starfish are in some cases taken from their habitat and sold to tourists as souvenirs, ornaments, curios or for display in aquariums. Starfish_sentence_312

In particular, Oreaster reticulatus, with its easily accessed habitat and conspicuous coloration, is widely collected in the Caribbean. Starfish_sentence_313

In the early to mid 20th century, this species was common along the coasts of the West Indies, but collection and trade have severely reduced its numbers. Starfish_sentence_314

In the State of Florida, O. reticulatus is listed as endangered and its collection is illegal. Starfish_sentence_315

Nevertheless, it is still sold throughout its range and beyond. Starfish_sentence_316

A similar phenomenon exists in the Indo-Pacific for species such as Protoreaster nodosus. Starfish_sentence_317

In industry and military history Starfish_section_31

With its multiple arms, the starfish provides a popular metaphor for computer networks, companies and software tools. Starfish_sentence_318

It is also the name of a seabed imaging system and company. Starfish_sentence_319

Starfish has repeatedly been chosen as a name in military history. Starfish_sentence_320

Three ships of the Royal Navy have borne the name HMS Starfish: an A-class destroyer launched in 1894; an R-class destroyer launched in 1916; and an S-class submarine launched in 1933 and lost in 1940. Starfish_sentence_321

In the World War II, Starfish sites were large-scale night-time decoys created during The Blitz to simulate burning British cities. Starfish_sentence_322

Starfish Prime was a high-altitude nuclear test conducted by the United States on 9 July 1962. Starfish_sentence_323


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Starfish.