Starfish areechinoderms and typically have a central disc and usually five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish havetube feet operated by ahydraulic system and a mouth at the centre of the oral or lower surface. They areopportunistic feeders and are mostlypredators onbenthic invertebrates. Several species have specialized feeding behaviours including eversion of their stomachs andsuspension feeding. They have complexlife cycles and can reproduce both sexually andasexually. Most canregenerate damaged parts or lost arms and they can shed arms as a means of defense.
Thefossil record for starfish is ancient, dating back to theOrdovician period around 450 million years ago, but it is rather sparse, as starfish tend to disintegrate after death. Only theossicles and spines of the animal are likely to be preserved, making remains hard to locate. With their appealing symmetrical shape, starfish have played a part in literature and legend. They are sometimes collected ascurios, used in design or as logos, and in some cultures they are eaten.
Anatomy
Most starfish have five arms that radiate from a central disc, but the number varies with the group. Some species have six or seven arms and others have 10–15 arms.[3] In AntarcticLabidiaster annulatus, the number of arms can exceed fifty.[4] Evidence fromgene expression finds that the starfish body corresponds to a head externally (with lips attached to the tube feet) and atorso internally.[5] Starfish possess twovascular systems, one for transport of water to support locomotion and other functions, and another for circulation of blood.
Body wall
The body wall layers include a thin cuticle, anepidermis consisting of a single layer of cells, a thickdermis formed ofconnective tissue, a thincoelomicmyoepithelial layer for the muscles, and aperitoneum. The dermis contains anendoskeleton ofcalcium carbonate components known as ossicles. These are honeycomb-like structures composed ofcalcite microcrystals arranged in a lattice.[6] They vary in form, from flat plates to granules to spines, and cover the aboral surface.[7] Some are specialised structures such as themadreporite (the entrance to the water vascular system),pedicellariae, andpaxillae. Paxillae are umbrella-like structures found on starfish that live buried in substrate. 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. The ossicles are located under the epidermal layer, even those emerging externally.[6]
Several groups of starfish, includingValvatida andForcipulatida, possess pedicellariae.[8] These are scissor-like ossicles at the tip of the spine which displace organisms from resting on the starfish's surface.[9][10] Some species likeLabidiaster annulatus andNovodinia antillensis use their pedicellariae to catch prey.[11] There may also bepapulae, thin-walled protrusions of the body cavity that reach through the body wall into the surrounding water. These serve arespiratory function.[12] 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 theinterstices. This arrangement enables both easy flexion of the arms and the rapid onset of stiffness and rigidity required for some actions performed under stress.[13]
The watervascular system of the starfish is ahydraulic system made up of a network of fluid-filled canals and is concerned with locomotion, adhesion, food manipulation andgas exchange. Water enters the system through themadreporite, a porous, often conspicuous, sieve-like ossicle on the aboral surface. It is linked through acalcareous-lined canal called the stone canal, to a ring canal around the mouth opening. A set of radial canals branch off from the ring canal; one radial canal runs along theambulacral groove in each arm. There are short lateral canals branching off alternately to either side of the radial canal, each ending in an ampulla. 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. 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. The interior of the whole canal system is lined withcilia.[14]
Water is pushed into the tube face when longitudinal muscles in the ampullae contract, and shut the valves in the lateral canals. This causes the tube feet to stretch and touch thesubstrate.[14] Although the tube feet resemble suction cups in appearance, the gripping action is a function of adhesive chemicals rather than suction.[15] Other chemicals and relaxation of the ampullae allow for release from the substrate. The tube feet latch on to surfaces and move in a wave, with one arm section attaching to the surface as another releases.[16][17] To expose the sensory tube feet and the eyespot to external stimuli, some starfish turn up the tips of their arms while moving.[18]
Having descended frombilateral organisms, starfish may move in a bilateral fashion, particularly when hunting or threatened. When crawling, certain arms act as the leading arms, while others trail behind. When a starfish finds itself upside down, two adjacent arms and an opposite arm press against the ground to lift up the two remaining arms; the opposite arm leaves the ground as the starfish turns over and recovers its normal stance.[19]
Apart from their function in locomotion, the tube feet act as accessory gills. The water vascular system serves to transportoxygen from, and carbon dioxide to, the tube feet and nutrients from the gut to the muscles involved in locomotion. Fluid movement is bidirectional and initiated by cilia.[14]
Video showing the tube feet movement of a starfish
The gut of a starfish fills most of the central disc and extends into the arms. The mouth occupies the centre of the oral surface, where it is surrounded by a toughperistomial membrane and closed with asphincter. A shortoesophagus connects the mouth to astomach, which consists of aneversible cardial portion and a smallerpyloric portion. The cardial stomach is glandular and pouched, and is supported byligaments attached to ossicles in the arms so it can be pulled back into position after it has been everted. The pyloric stomach has two extensions into each arm: the pyloric caeca. These are long, hollow tubes lined by a series of glands which secrete digestiveenzymes and absorb nutrients from the food. A shortintestine andrectum run from the pyloric stomach to theanus at the apex of the aboral surface of the disc.[20]
Primitive starfish, such asAstropecten andLuidia, swallow theirprey whole, and start to digest it in their cardial stomachs, spitting out hard material like shells. The semi-digested fluid flows into the caeca for more digestion as well as absorption.[20] In more advanced species of starfish, the cardial stomach can be everted from the organism's body to engulf and digest food, which is passed to the pyloric stomach.[21][16] The retraction and contraction of the cardial stomach is activated by aneuropeptide known as NGFFYamide.[22]
The main nitrogenous waste product isammonia, which is removed viadiffusion through the tube feet, papulae and other thin-walled areas. Other waste material includeurates. The body fluid containsphagocytic cells calledcoelomocytes, which are also found within the hemal and water vascular systems. 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.[23]
Starfish keep their body fluids at the same salt concentration as the surrounding water, the lack of an osmoregulation system probably explains why starfish are not found in fresh water and rarely inestuarine environments.[23]
Sensory and nervous systems
Although starfish do not have many well-defined sense organs, they do perceive touch, light, temperature, orientation and the status of the water around them. The tube feet, spines and pedicellariae are sensitive to touch. 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.[21] There are eyespots at the ends of the arms, each one made of 80–200 simpleocelli composed ofpigmented epithelial cells. Individualphotoreceptor cells are present in other parts of their bodies and respond to light. Whether they advance or retreat depends on the species.[24]
While a starfish lacks acentralized brain, it has a complexnervous 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. The peripheral nerve system consists of two nerve nets: one in the epidermis and the other in the lining of the coelomic cavity, which are the sensory and motor systems respectively. Neurons passing through the dermis join the two. Both the ring and radial nerves function in movement and sensory. The sensory component is supplied with information from the sensory organs while the motor nerves control the tube feet and musculature. If one arm detects something attractive, it becomes dominant and temporarily over-rides the other arms to initiate movement towards it.[24]
Circulatory and gas exchange system
The body cavity contains thecirculatory or haemal system. 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). 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. Blood does not contain a pigment such asheme, but is probably used to transport nutrients around the body.[23] Gas exchange mainly takes place throughgills known as papulae, which are thin-walled bulges along the aboral surface of the arms. Oxygen is transferred from these to thecoelomic fluid, which moves gas around the body.[14]
Secondary metabolites
Starfish produce a large number ofsecondary metabolites in the form oflipids, includingsteroidal derivatives ofcholesterol, andfatty acidamides ofsphingosine. The steroids are mostlysaponins, known as asterosaponins, and theirsulphated derivatives. They vary across species and are typically formed from up to six sugar molecules (usuallyglucose andgalactose) connected by up to threeglycosidic chains. Long-chain fatty acid amides of sphingosine occur frequently, with some having knownbiological activity. Starfish also contain variousceramides and a small number ofalkaloids. These chemicals in the starfish may function in defence and communication. Some are feeding deterrents used by the starfish to discourage predation. Others areantifoulants and supplement the pedicellariae to prevent other organisms from settling on the starfish's aboral surface. Some are alarmpheromones and escape-eliciting chemicals, the release of which trigger responses in starfish of the same species, but often stimulate flight in potential prey.[25] Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide.[26]
Life cycle
Sexual reproduction
Most species of starfish aregonochorous, there being separate male and female individuals.[27] Some species aresimultaneous hermaphrodites, producing eggs and sperm at the same time, and in a few of these the same gonad, called anovotestis, produces both eggs and sperm.[28] Other starfish aresequential hermaphrodites.Protandrous individuals of species likeAsterina gibbosa start life as males before changing sex into females as they grow older.[29] In some species such asNepanthia belcheri, a large female cansplit in half and the resulting offspring are males. When these grow large enough they change back into females.[30]
Each starfish arm contains two gonads that releasegametes through openings called gonoducts, located on the central disc between the arms.Fertilization is generally external[27] but in a few species, internal fertilization takes place.[28] In most species, the buoyant eggs and sperm are simply released into the water (free spawning) and the resultingembryos andlarvae live as part of theplankton.[27] In others, the eggs may be stuck to the undersides of rocks.[29] In certain species of starfish, the femalesbrood their eggs – either by simply enveloping them or by holding them in specialised structures in different parts of the body, externally or internally.[31][32][27] Those starfish that brood their eggs by "sitting" on them usually assume a humped posture with their discs raised off the substrate.[33][29]Pteraster militaris broods a few of its young and disperses the remaining eggs, that are too numerous to fit into its pouch.[31] In these brooding species, the eggs are relatively large, and supplied withyolk, and they generally develop directly into miniature starfish without an intervening larval stage,[28] called "lecithotrophic" .[34] InParvulastra parvivipara, anintragonadal brooder, the young starfish obtain nutrients by eating other eggs and embryos in the brood pouch.[35] Brooding occurs in species that live in colder waters.[27] and in smaller species that produce just a few eggs.[36][37]
The timing of spawning may be influenced by lighting conditions, water temperature, food availability, and other factors. Individuals may gather together to release their gametes as once, usingpheromones to attract each other.[38][37] In some species, a male and female may come together and form a pair.[39][40] They engage inpseudocopulation which involves the male crawling on the female and fertilising her gametes as she releases them.[41][37]
Starfish embryos typically hatch asblastulas.Invaginations take place, the first forming the anus is created from theblastopore, while a second, taking place in the ectodermic layer, creates the mouth. Thearchenteron stretches towards the mouth and connects with it, forming the gut.[42] A band ofcilia develops on the exterior. This enlarges and extends around the surface and eventually onto two developing arm-like outgrowths. At this stage the larva is known as abipinnaria. The cilia are used for locomotion and feeding, their rhythmic beat waftingphytoplankton towards the mouth.[8]
The next stage in development is abrachiolaria larva, and involves the growth of three short ventral-anterior arms with adhesive tips surrounding a sucker. Both bipinnaria and brachiolaria larvae are bilaterally symmetrical. When fully developed, the brachiolaria settles on the seabed and attaches itself with a short stalk made from its ventral arms and sucker. Metamorphosis now takes place with a radical rearrangement of tissues. The larvae develops an oral surface on the left and an aboral surface on the right. While the gut remains, the mouth and anus move to new positions. Some of the body cavities disappear while others become the water vascular system and the visceral coelom. The starfish is now pentaradially symmetrical. It casts off its stalk and becomes a free-living juvenile starfish up to 1 mm (0.04 in) in diameter.[8]
Asexual reproduction
"Comet" ofLinckia guildingi, showing starfish body regrowing from a single arm
Some species of starfish can reproduceasexually as adults either byfission of their central discs or byautotomy (self-amputation) of one or more of their arms.[43][44] Single arms that regenerate a whole individual are called comet forms.[45] The larvae of several species of starfish can reproduce asexually before they reach maturity.[46] They do this by autotomising some parts of their bodies or bybudding.[47] Larva increase asexual reproduction when they sense that food is plentiful.[48] 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.[47]
Some species of starfish have the ability toregenerate lost arms and can regrow an entire new limb given time.[49] 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.[23] Regrowth can take several months, and starfish are vulnerable to infections during the early stages after the loss of an arm.[49] Other than fragmentation carried out for the purpose of reproduction, the division of the body may happen as adefense mechanism.[23] The loss of body parts is achieved by the rapid softening of a special type of connective tissue in response to nervous signals. This type of tissue is calledcatch connective tissue and is found in mostechinoderms.[50] An autotomy-promoting factor has been identified which, when injected into another starfish, causes rapid shedding of arms.[51]
Lifespan
The lifespan of a starfish varies considerably among species. For example,Leptasterias hexactis reaches sexual maturity at 20 g (0.7 oz) in two years and lives for about ten years.Pisaster ochraceus matures at 70–90 g (2.5–3.2 oz) in five years and has a maximum recorded lifespan of 34 years.[8]
Ecology
Distribution and habitat
Starfish live in marine waters around the world including both tropical and polar waters.[6][52][53] They are mainlybenthic animals, living in sandy, muddy and rocky substrates.[6][16] They range from shallow,intertidal waters[52] to the deep-sea floor down to at least 6,000 m (20,000 ft).[54] Starfish are most common along the coast.[6]
Most species are generalist predators, eatingmicroalgae,sponges,bivalves,snails and other small animals.[21][55] Thecrown-of-thorns starfish consumescoral polyps,[56] while other species aredetritivores, feeding on decomposing organic material and faecal matter.[55][52] A few are suspension feeders, gathering inphytoplankton;Henricia andEchinaster often feed with sponges, taking advantage of the water current they produce. Various species can absorb organic nutrients from the surrounding water, and this may form a significant portion of their diet.[57]
The processes of feeding and capture may be aided by special parts;Pisaster brevispinus, the short-spined pisaster from theWest Coast of America, can use a set of specialized tube feet to dig itself deep into the soft substrate to extract prey (usuallyclams).[58] Grasping the shellfish, the starfish slowly pries open the prey's shell, overcoming the clam'sadductor muscle, and inserts its everted stomach into the crack to digest the soft tissues. The gap between the clam'svalves need only be a fraction of a millimetre wide for the stomach to gain entry.[16]
Ecological impact
Starfish on a wood pier
Starfish arekeystone species in their respective marinecommunities. Their relatively large sizes, diverse diets, and ability to adapt to different environments makes them ecologically important.[59] The term "keystone species" was in fact first used byRobert Paine in 1966 to describe a starfish,Pisaster ochraceus.[60] When studying the low intertidal coasts ofWashington state, Paine found that predation byP. ochraceus was a major factor in the diversity of species. Experimental removals of this top predator from a stretch of shoreline resulted in lower species diversity and the eventual domination ofMytilus mussels, which were able to outcompete other organisms for space and resources.[61] Similar results were found in a 1971 study ofStichaster australis on the intertidal coast of theSouth Island ofNew Zealand.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 whichS. australis had been removed, the mussels increased in number dramatically, overwhelming the area and threateningbiodiversity.[62]
Pisaster ochraceus consuming a mussel in centralCalifornia
The feeding activity of theomnivorous starfishOreaster reticulatus on sandy and seagrass bottoms near theVirgin Islands effects the composition of communities of microorganisms. These starfish engulf piles of sediment removing the surface films and algae adhering to the particles. Organisms that dislike this disturbance are replaced by others better able to rapidly recolonise "clean" sediment. In addition, foraging by these starfish creates diverse patches of organic matter, which may attract larger organisms such as fish, crabs and sea urchins that feed on the sediment.[63][64][65]
Starfish sometimes have negative effects on ecosystems. Outbreaks of crown-of-thorns starfish have caused damage to coral reefs in Northeast Australia andFrench Polynesia.[56][66] A study in Polynesia found that coral cover declined drastically with the arrival of migratory starfish in 2006, dropping over 40% to under 5% in four years. This in turn had acascade effect on both sessile bottom-dwelling animals and reef fish.[56]Asterias amurensis is a rare example of aninvasive echinoderm . Its larvae likely arrived inTasmania from central Japan via water discharged from ships in the 1980s. The species has since grown in numbers to the point where they threaten importantbivalve fisheries in Australia. As such, they are considered pests,[67] and are on the Invasive Species Specialist Group'slist of the world's 100 worst invasive species.[68] Some species that prey onbivalve molluscs can transmitparalytic shellfish poisoning.[69]
Several species sometimes suffer from awasting condition caused byVibrio bacteria.[71] A more widespreadsea star wasting disease sporadically causesmass mortalities.[76] The results of a 2025 study of starfish off the coast of centralBritish Columbia suggest that those living in thefjords can better survive outbreaks of the disease due to the lower temperatures and higher salinity of their environment.[77][78]
The protozoanOrchitophrya stellarum is known to infect and damage the gonads of starfish.[71] Starfish are vulnerable to high temperatures. Experiments have shown that the feeding and growth rates ofP. 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).[79][80][71] This species has a unique ability to absorb seawater to keep itself cool when it is exposed to sunlight by a receding tide.[81] It also appears to rely on its arms to absorb heat, so as to protect the central disc and vital organs.[82]
Starfish and other echinoderms can be vulnerable tomarine pollution.[83] Thecommon starfish is considered to be abioindicator species for marine ecosystems.[84] A 2009 study found thatP. ochraceus is unlikely to be affected byocean acidification as severely as other marine animals withcalcareous skeletons. In other groups, structures made of calcium carbonate are vulnerable to dissolution when thepH is lowered. Researchers found that whenP. ochraceus were exposed to 21 °C (70 °F) and 770 ppmcarbon dioxide (beyond rises expected in the next century), they were relatively unaffected. 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.[85]
The earliest fossil echinoderms date to theCambrian, with the first asterozoans (a group that includes starfish and brittle stars) being theSomasteroidea, which exhibit traits of both groups.[86] Starfish are infrequently found as fossils, possibly because their hard skeletal components separate as the animal decays. Despite this, there are a few places where accumulations of complete skeletal structures occur, fossilized in place inLagerstätten – so-called "starfish beds".[87]
By the latePaleozoic, thecrinoids andblastoids were the predominant echinoderms, fragments of which are almost the only fossil found in some limestones. In the two majorextinction events that occurred during the lateDevonian and latePermian, the blastoids were wiped out and only a few species of crinoids survived.[86] Many starfish species also became extinct in these events, but afterwards the surviving few species quickly diversified rapidly over sixty million years between the beginning and middle of theMiddle Jurassic.[88][89] A 2012 study found thatspeciation in starfish can occur rapidly. During the last 6,000 years, divergence in the larval development ofCryptasterina hystera andCryptasterina pentagona has taken place, the former adopting internal fertilization and brooding and the latter remaining a broadcast spawner.[90]
The scientific name Asteroidea was given to starfish by the French zoologistde Blainville in 1830.[91] It is derived from the Greekaster, ἀστήρ (a star) and the Greekeidos, εἶδος (form, likeness, appearance).[92] Starfish are included in the subphylumAsterozoa along with brittle and basket stars (orderOphiuroidea), the characteristics of which include a star-shaped body as adults, with multiple arms surrounding central disc. The arms of asteroids are skeletally connected to the disc by ossicles in the body wall[88] while ophiuroids have clearly demarcated arms.[93]
The starfish are a large and diverse class with over 1,900 living species. There are sevenextant orders:Brisingida,Forcipulatida,Notomyotida,Paxillosida,Spinulosida,Valvatida andVelatida.[2][1] Living asteroids, the Neoasteroidea, are distinct from their forerunners in the Paleozoic. Their classification has changed little but there is debate in regards to Paxillosida. The deep-watersea daisies, though clearly Asteroidea and currently included inVelatida, do not fit easily in any accepted lineage.Phylogenetic data suggests that they may be asister group, the Concentricycloidea, to the Neoasteroidea, or that the Velatida themselves may be a sister group.[89]
Species in this order have a small, rigid disc and 6–20 long, thin arms, which they use for suspension feeding. They have one series of marginal plates, disc plates merged in a ring, fewer numbers of aboral plates, crossed pedicellariae, and several series of long spines on the arms. They mostly live in deep-sea habitats, although a few live in shallow waters in the Antarctic.[95][96] In some species, the tube feet have rounded tips and lack suckers.[97]
Species in this order have distinctivepedicellariae, consisting of a short stalk with forceps-like tips. and tube feet with flat-tipped suckers usually arranged in four rows.[97][8][88] The order includes well-known species from temperate and cold-water regions, ranging from intertidal to abyssal zones.[99]
These starfish are deep-sea dwelling and have particularly flexible arms with distinctive lines of musculature along the sides of the dorsal region.[1] In some species, the tube feet lack suckers.[97]
This is a primitive order whose members do not extrude their stomach[20] when feeding and both anus and tube feet suckers are absent.[102] Papulae are present on their aboral surface, and they possess marginal plates and paxillae. They mostly inhabit soft substrates.[8] There is no brachiolaria stage in their larval development.[102] The comb starfish (Astropecten polyacanthus) is a member of this order.[103]
Most species in this order lack pedicellariae; all have a delicate skeletal arrangement with small or no marginal plates on the disc or arms. They have numerous groups of short spines on the aboral surface.[105][106]
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 havepaxillae and in some, the main pedicellariae are clamp-like and recessed into the skeletal plates.[106]
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. The skeleton is underdeveloped.[109]
Starfish aredeuterostome animals, like thechordates. A 2014 analysis of 219 genes from all classes of echinoderms gives the followingphylogenetic tree.[112] The times at which theclades diverged are shown under the labels in millions of years ago (mya).
The phylogeny of the Asteroidea has been difficult to resolve, with visible (morphological) features proving inadequate, and the question of whether traditionaltaxa areclades apply.[2] The phylogeny proposed by Gale in 1987 is:[2][113]
† Palaeozoic Asteroids
Paxillosida
Forcipulatida, including Brisingida
Valvatida, including Velatida, Spinulosida(not a clade)[2]
The phylogeny proposed by Blake in 1987 is:[2][114]
† Palaeozoic Asteroids
† Calliasterellidae
† Compasteridae
† Trichasteropsida
Brisingida
Forcipulatida
Spinulosida
Velatida
Paxillosida
Notomyotida
Valvatida
Later work making use ofmolecular evidence, with or without the use of morphological evidence, had by 2000 failed to resolve the argument.[2] 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". 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. The Solasteridae are split from the Velatida, and the old Spinulosida is broken up.[115]
Velatida except for Solasteridae
Brisingida with part of Velatida, e.g.Caymanostella and part of Forcipulatida, e.g.Stichaster
Forcipulatida
part of Spinulosida, e.g.Echinaster, part of Valvatida, e.g.Archaster
Paxillosida
Odontasteridae, which was a part of Valvatida
Solasteridae and part of Spinulosida, e.g.Stegnaster and part of Valvatida, e.g.Asterina
Starfish have been used in reproductive and developmental studies. Female starfish produce large numbers ofoocytes that are easily isolated; these can be stored in apre-meiosis phase and stimulated to complete division by the use of1-methyladenine.[116] Starfish oocytes are well suited for this research as they are easy to handle, can be maintained in sea water at room temperature, are transparent, and develop quickly.[117]Asterina pectinifera, used as amodel organism for this purpose, is resilient and easy to breed and maintain in the laboratory.[118]
Another area of research is the ability of starfish to regenerate lost body parts. Thestem 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.[119]
Starfish have an unusual ability to displace foreign objects from their bodies, which makes them difficult to tag for research tracking purposes.[120]
In legend and culture
A starfish with five legs. Used as an illustration of "Hope in God", a poem by Lydia Sigourney which appeared inPoems for the Sea, 1850
Anaboriginal Australian fable, retold by the Welsh school headmasterWilliam Jenkyn Thomas (1870–1959),[121] tells how some animals needed a canoe to cross the ocean. 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. When Whale realized the trick he beat Starfish ragged, which is how Starfish still is today.[122]
In 1900, the scholarEdward Tregear documentedThe Creation Song, which he describes as "an ancient prayer for the dedication of a high chief" ofHawaii. Among the "uncreated gods" described early in the song is the starfish.[123]
Georg Eberhard Rumpf's 1705The Ambonese Curiosity Cabinet describes the tropical varieties ofStella Marina orBintang Laut, "Sea Star" in Latin andMalay respectively, known in the waters aroundAmbon. He writes that theHistoire 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".[124]
As food
Fried starfish skewers in China
Starfish are sometimes eaten in China,[125] Japan[126][127] and in Micronesia.[128] Georg Eberhard Rumpf found few starfish being used for food in theIndonesian 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 sourtamarind leaves; after resting the pieces for a day or two, they remove the outer skin and cook them incoconut milk.[124]
As collectables
Starfish are in some cases taken from their habitat and sold to tourists assouvenirs,ornaments, curios or for display in aquariums. In particular,Oreaster reticulatus, with its easily accessed habitat and bright coloration, is widely collected in the Caribbean. In the early to mid 20th century, this species was numerous along the West Indian coasts, but collection and trade have severely diminished its numbers. In theState of Florida,O. reticulatus is listed asendangered and its collection is illegal. Nevertheless, it is still sold both in and outside its range.[65] A similar phenomenon exists in the Indo-Pacific for species such asProtoreaster nodosus.[129]
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