Starfish

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.{{cite arXiv |eprint=1202.2219|last1=Wu|first1=Liang|title=The advantages of the pentameral symmetry of the starfish|last2=Ji|first2=Chengcheng|last3=Wang|first3=Sishuo|last4=Lv|first4=Jianhao|class=q-bio.PE|year=2012}} In Antarctic Labidiaster annulatus the number of arms can reach over fifty.{{cite book|author=Prager, Ellen|year=2011|title=Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter|publisher=University of Chicago Press|page=74|isbn=978-0-2266-7872-6}} Evidence from gene expression finds that the starfish body corresponds to a head externally (with lips attacted to the tube feet) and a torso internally.{{cite journal|last1=Lacalli|first=T|year=2023|title=A radical evolutionary makeover gave echinoderms their unusual body plan|journal=Nature|volume=623|issue=7987|pages=485–486|doi=10.1038/d41586-023-03123-1}}

The body wall layers include a thin cuticle, an epidermis consisting of a single layer of cells, a thick dermis formed of connective tissue and thin coelomic myoepithelial layer for the muscles, and a peritoneum. The dermis contains an endoskeleton of calcium carbonate components known as ossicles. These are honeycomb-like structures composed of calcite microcrystals arranged in a lattice.Ruppert et al., 2004. pp. 876–880 They vary in form, from flat plates to granules to spines, and cover the aboral surface.{{cite web |url=http://www.sms.si.edu/IRLSpec/Phyl_Echino_Glossary.htm |title=Glossary of terms: Phylum Echinodermata |author=Sweat, L. H. |date=2012-10-31 |publisher=Smithsonian Institution |access-date=2013-05-12|archive-url=

https://web.archive.org/web/20160304203303/http://www.sms.si.edu/IRLSpec/Phyl_Echino_Glossary.htm|archive-date=4 March 2016|url-status=dead}} Some are specialised structures such as the madreporite (the entrance to the water vascular system), pedicellariae and paxillae. 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.

Several groups of starfish, including Valvatida and Forcipulatida, possess pedicellariae. These are scissor-like ossicles at the tip of the spine which displace organisms from resting on the starfish's surface.{{cite book | title=The Invertebrates: a new synthesis | author=Barnes, R. S. K. |author2=Callow, P. |author3=Olive, P. J. W. | year=1988 | publisher=Blackwell Scientific Publications | location=Oxford | isbn=978-0-632-03125-2 | pages=158–160}}{{cite web | url=http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasPedi.php | title=Pedicellariae | publisher=A Snail's Odyssey | work=Sea Stars: Predators & Defenses | access-date=2013-05-11 | author=Carefoot, Tom | archive-url=https://web.archive.org/web/20130316010647/http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasPedi.php | archive-date=16 March 2013 | url-status=dead}} Some species like Labidiaster annulatus and Novodinia antillensis use their pedicellariae to catch prey.{{cite book|title=Starfish: Biology and Ecology of the Asteroidea |author = Lawrence, J. M. | contribution = The Asteroid Arm |url=https://books.google.com/books?id=yY-5OsDZ9H8C&pg=PA15 | pages=15–23|isbn = 9781421407876 |date = 2013-01-24 |publisher = JHU Press }} in Lawrence (2013) There may also be papulae, thin-walled protrusions of the body cavity that reach through the body wall and extend into the surrounding water. These serve a respiratory function. 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 interstices. 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.{{cite journal |author=O'Neill, P. |year=1989 |title=Structure and mechanics of starfish body wall |journal=Journal of Experimental Biology |volume=147 |pages=53–89 |doi=10.1242/jeb.147.1.53 |pmid=2614339 }}

File:Luidia maculata, Ras Sedr, Egypt.jpg|Luidia maculata, a seven armed starfish

File:Astropecten aranciacus Naxos08 1775 dett.jpg|Astropecten aranciacus ossicles

File:Pédicellaires d' Acanthaster Planci.JPG|Pedicellariae and retracted papulae among the spines of Acanthaster planci

File:Asterias forbesi pedicellaria and papulae.jpg|Pedicellaria and papulae of Asterias forbesi

File:Détail bras d'étoile de mer.jpg showing tube feet and eyespot]]

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. Water enters the system through the madreporite, a porous, often conspicuous, sieve-like ossicle on the aboral surface. It is linked through a stone canal, often lined with calcareous material, to a ring canal around the mouth opening. A set of radial canals leads off this; one radial canal runs along the ambulacral 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 with cilia.Ruppert et al., 2004. pp. 879–883, 889

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 the substrate. Although the tube feet resemble suction cups in appearance, the gripping action is a function of adhesive chemicals rather than suction.{{cite journal |author1=Hennebert, E. |author2=Santos, R. |author3=Flammang, P. |year=2012 |title=Echinoderms don't suck: evidence against the involvement of suction in tube foot attachment |journal=Zoosymposia |volume=1 |pages=25–32 |url=http://www.mapress.com/zoosymposia/content/2012/v7/f/v007p025-032f.pdf |doi=10.11646/zoosymposia.7.1.3 }} 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.{{cite journal|doi=10.1007/BF00210108 |title=Specializations for excitation-contraction coupling in the podial retractor cells of the starfish Stylasterias forreri |year=1981 |last1=Cavey |first1=Michael J. |last2=Wood |first2=Richard L. |journal=Cell and Tissue Research |volume=218 |issue=3 |pages=475–485 |pmid=7196288 |s2cid=21844282 }} To expose the sensory tube feet and the eyespot to external stimuli, some starfish turn up the tips of their arms while moving.{{cite web | url=http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasTube.php | title=Tube feet | publisher=A Snail's Odyssey | work=Sea Stars: Locomotion | access-date=2013-05-11 | author=Carefoot, Tom | archive-url=https://web.archive.org/web/20131021181550/http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasTube.php | archive-date=21 October 2013 | url-status=dead}}

Having descended from bilateral organisms, starfish may move in a bilateral fashion, particularly when hunting or threated. When crawling, certain arms act as the leading arms, while others trail behind. When a starfish finds itself upside down, its raises its arms and then two adjacent arms and an opposite arm along press against the ground to lift up the two remaining arms; the opposite arm leaves the ground as the starfish turns itself over and recovers its normal stance.{{cite journal |author1=Chengcheng, J. |author2=Wu, L. |author3=Zhoa, W. |author4=Wang, S. |author5=Lv, J. |year=2012 |title=Echinoderms have bilateral tendencies |journal=PLOS ONE |volume=7 |issue=1 |page=e28978 |doi=10.1371/journal.pone.0028978 |pmid=22247765 |pmc=3256158 |arxiv=1202.4214 |bibcode=2012PLoSO...728978J |doi-access=free }}

Apart from their function in locomotion, the tube feet act as accessory gills. 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. Fluid movement is bidirectional and initiated by cilia.

File:Asterias rubens, dissection.svg:

{{image key

|list type=ordered

|Pyloric stomach

|Intestine and anus

|Rectal sac

|Stone canal

|Madreporite

|Pyloric caecum

|Digestive glands

|Cardiac stomach

|Gonad

|Radial canal

|Ambulacral ridge}}]]

The gut of a starfish fills most of the disc and extends into the arms. The mouth is occupies the centre of the oral surface, where it is surrounded by a tough peristomial membrane and closed with a sphincter. A short oesophagus connects the mouth to a stomach which consists of an eversible cardiac portion and a smaller pyloric portion. 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. The pyloric stomach has two extensions into each arm: the pyloric caeca. These long, hollow tubes that are lined by a series of glands, which secrete digestive enzymes and absorb nutrients from the food. A short intestine and rectum run from the pyloric stomach to the anus at the apex of the aboral surface of the disc.Ruppert et al., 2004. p. 885

Primitive starfish, such as Astropecten and Luidia, shallow their prey whole, and start to digest it in their cardiac stomachs, spitting out hard material like shells. The semi-digested fluid flows into the caeca for more digestion as well as absorption. In more advanced species of starfish, the cardiac stomach can be everted from the organism's body to engulf and digest food. 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, to engulf and digest the prey, which is passed to the pyloric stomach.{{cite web | url=http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasAdul.php | title=Adult feeding | publisher=A Snail's Odyssey | work=Sea Stars: Feeding, growth, & regeneration | access-date=2013-07-13 | author=Carefoot, Tom | archive-url=https://web.archive.org/web/20130512053338/http://www.asnailsodyssey.com/LEARNABOUT/SEASTAR/seasAdul.php | archive-date=12 May 2013 | url-status=dead}} The retraction and contraction of the cardiac stomach is activated by a neuropeptide known as NGFFYamide.{{cite journal|author1=Semmens, Dean C. |author2=Dane, Robyn E. |author3=Pancholi, Mahesh R. |author4=Slade, Susan E. |author5=Scrivens, James H. |author6=Elphick, Maurice R. |year=2013|title=Discovery of a novel neurophysin-associated neuropeptide that triggers cardiac stomach contraction and retraction in starfish |journal=Journal of Experimental Biology |doi=10.1242/jeb.092171 |volume=216 |issue=21 |pages=4047–4053 |pmid=23913946 |s2cid=19175526 |doi-access=free }}

The main nitrogenous waste product is ammonia, which is removed diffusion through the tube feet, papulae and other thin-walled areas. Other waste material include urates. Their body fluid contains phagocytic cells called coelomocytes, 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.Ruppert et al., 2004. pp. 886–887

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 or even in many estuarine environments.

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. 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. There are eyespots at the ends of the arms, each one made of 80–200 simple ocelli composed of pigmented epithelial cells. Individual photoreceptor cells are present in other parts of their bodies and respond to light. Whether they advance or retreat depends on the species.Ruppert et al., 2004. pp. 883–884

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. 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, it becomes dominant and temporarily over-rides the other arms to initiate movement towards it.

The body cavity contains the circulatory 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 but is probably used to transport nutrients around the body. Gas exchange aminly takes place through gills known as papulae, which are thin-walled bulges along the aboral surface of the arms. Oxygen is transferred from these to the coelomic fluid, which moves gas around the body.

Starfish produce a large number of secondary metabolites in the form of lipids, including steroidal derivatives of cholesterol, and fatty acid amides of sphingosine. The steroids are mostly saponins, known as asterosaponins, and their sulphated derivatives. 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. Long-chain fatty acid amides of sphingosine occur frequently with some having known biological activity. Starfish also contain various ceramides and a small number of alkaloids. These these chemicals in the starfish may function in defence and communication. Some are feeding deterrents used by the starfish to discourage predation. Others are antifoulants and supplement the pedicellariae to prevent other organisms from settling on the starfish's aboral surface. Some are alarm pheromones and escape-eliciting chemicals, the release of which trigger responses in conspecific starfish but often stimulate flight in potential prey.{{cite book |chapter=8: Chemistry and Ecological Role of Starfish Secondary Metabolites |title=Starfish: Biology and Ecology of the Asteroidea |editor-last=Lawrence |editor-first=John M. |last1=McClintock |first1=James B. |last2=Amsler |first2=Charles D. |last3=Baker | first3=Bill J. |year=2013 |publisher=JHU Press |pages=81–89|isbn=978-1-4214-1045-6 |chapter-url=https://books.google.com/books?id=WQDvIQ5xR68C&q=%22+secondary+metabolite%22+starfish&pg=PT154 }} Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide.{{cite journal |author1=Zhang, Wen |author2=Guo, Yue-Wei |author3=Gu, Yucheng |year=2006 |title=Secondary metabolites from the South China Sea invertebrates: chemistry and biological activity |journal=Current Medicinal Chemistry |volume=13 |issue=17 |pages=2041–2090 |doi=10.2174/092986706777584960 |pmid=16842196 }}

Most species of starfish are gonochorous, there being separate male and female individuals. 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.{{Cite journal |doi=10.2307/3593116 |volume=208 |issue=2 |pages=81–91 |last=Byrne |first=Maria |title=Viviparity in the sea star Cryptasterina hystera (Asterinidae): conserved and modified features in reproduction and development |journal=Biological Bulletin |year=2005| pmid=15837957 |jstor=3593116 |citeseerx=10.1.1.334.314 |s2cid=16302535}} Other starfish are sequential hermaphrodites. Protandrous individuals of species like Asterina gibbosa start life as males before changing sex into females as they grow older. In some species such as Nepanthia belcheri, a large female can split in half and the resulting offspring are males. When these grow large enough they change back into females.{{Cite journal |doi = 10.1007/BF00397488 |volume=69 |issue=3 |pages=223–233 |author1=Ottesen, P. O. |author2=Lucas, J. S. | title = Divide or broadcast: interrelation of asexual and sexual reproduction in a population of the fissiparous hermaphroditic seastar Nepanthia belcheri (Asteroidea: Asterinidae) |journal=Marine Biology |year=1982 |bibcode=1982MarBi..69..223O |s2cid=84885523}}

Each starfish arm contains two gonads that release gametes through openings called gonoducts, located on the central disc between the arms. Fertilization is generally external but in a few species, internal fertilization takes place. 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. In others, the eggs may be stuck to the undersides of rocks.{{cite journal|author1=Crump, R. G. |author2=Emson, R. H. | title=The natural history, life history and ecology of the two British species of Asterina| journal=Field Studies| year=1983| volume=5| issue=5 |pages=867–882| url=http://fsj.field-studies-council.org/media/342971/vol5.5_160.pdf |access-date=2011-07-27 }} In certain species of starfish, the females brood their eggs – either by simply enveloping them or by holding them in specialised structures. Brooding may be done in pockets on the starfish's aboral surface,{{Cite journal |doi = 10.1007/BF00399585 | volume=103 |issue=4 |pages=531–540 |author1=McClary, D. J. |author2=Mladenov, P. V. |title = Reproductive pattern in the brooding and broadcasting sea star Pteraster militaris |journal = Marine Biology |year = 1989 | bibcode=1989MarBi.103..531M |s2cid = 84867808}} inside the pyloric stomach (Leptasterias tenera){{Cite journal| doi = 10.2307/1540983| volume = 162| issue = 3| pages = 273–289|author1=Hendler, Gordon |author2=Franz, David R. | title = The biology of a brooding seastar, Leptasterias tenera, in Block Island |jstor=1540983 | journal = Biological Bulletin| year= 1982| url = https://www.biodiversitylibrary.org/part/6370}} or even in the interior of the gonads themselves. Those starfish that brood their eggs by "sitting" on them usually assume a humped posture with their discs raised off the substrate.{{Cite journal| volume = 130| issue = 3| pages = 304–315| author= Chia, Fu-Shiang| title = Brooding behavior of a six-rayed starfish, Leptasterias hexactis| journal = Biological Bulletin| year = 1966 |jstor=1539738| doi = 10.2307/1539738| url = https://www.biodiversitylibrary.org/part/9408}} Pteraster militaris broods a few of its young and disperses the remaining eggs, that are too numerous to fit into its pouch. 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. 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. In Parvulastra parvivipara, an intragonadal brooder, the young starfish obtain nutrients by eating other eggs and embryos in the brood pouch.{{Cite journal | volume = 125 | issue = 3 |pages = 551–567| last=Byrne |first=M. | title = Viviparity and intragonadal cannibalism in the diminutive sea stars Patiriella vivipara and P. parvivipara (family Asterinidae) | journal = Marine Biology | year = 1996 | doi = 10.1007/BF00353268 | bibcode = 1996MarBi.125..551B | s2cid = 83110156 | url = https://link.springer.com/article/10.1007/BF00353268| url-access = subscription }} Brooding is especially common in species that live in colder waters.Ruppert et al., 2004. pp. 887–888 and in smaller species that produce just a few eggs.{{cite book |author1=Mercier, A. |author2=Hamel J-F. |contribution=Reproduction in Asteroidea |page=37 |title=Starfish: Biology and Ecology of the Asteroidea|date=2014 |volume=10 |issue=1 |doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013)

In the tropics, a plentiful supply of phytoplankton is continuously available for starfish larvae to feed on. Spawning takes place at any time of year, each species having its own characteristic breeding season.{{cite journal |author=Thorson, Gunnar |year=1950 |title=Reproductive and larval ecology of marine bottom invertebrates |journal=Biological Reviews |volume=25 |issue=1 |pages=1–45 |doi=10.1111/j.1469-185X.1950.tb00585.x |pmid=24537188 |s2cid=43678161 }} In temperate regions, the spring and summer brings an increase in food supplies. 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.{{cite journal |author1=Beach, D. H. |author2=Hanscomb, N. J. |author3=Ormond, R. F. G. |year=1975 |title=Spawning pheromone in crown-of-thorns starfish |journal=Nature |volume=254 |pages=135–136 |doi=10.1038/254135a0 |issue=5496 |pmid=1117997 |bibcode=1975Natur.254..135B |s2cid=4278163 }} In other species, a male and female may come together and form a pair.{{cite journal |author1=Bos A.R. |author2=G.S. Gumanao |author3=B. Mueller |author4=M.M. Saceda |year=2013 |title=Size at maturation, sex differences, and pair density during the mating season of the Indo-Pacific beach star Archaster typicus (Echinodermata: Asteroidea) in the Philippines |journal=Invertebrate Reproduction and Development |volume=57 |issue=2 |pages=113–119 |doi=10.1080/07924259.2012.689264 |bibcode=2013InvRD..57..113B |s2cid=84274160 |url=https://www.researchgate.net/publication/230851841 }}{{Cite journal| doi = 10.1007/BF00391987| issn = 0025-3162| volume = 99| issue = 2| pages = 247–253|author1=Run, J. -Q. |author2=Chen, C. -P. |author3=Chang, K. -H. |author4=Chia, F. -S. | title = Mating behaviour and reproductive cycle of Archaster typicus (Echinodermata: Asteroidea)| journal = Marine Biology|year=1988| bibcode = 1988MarBi..99..247R| s2cid = 84566087}} This behaviour is called pseudocopulation{{Cite journal| doi = 10.1007/s00227-011-1638-2 | volume = 158 | issue = 5 | pages = 1163–1173 |author1=Keesing, John K. |author2=Graham, Fiona |author3=Irvine, Tennille R. |author4=Crossing, Ryan | title = Synchronous aggregated pseudo-copulation of the sea star Archaster angulatus Müller & Troschel, 1842 (Echinodermata: Asteroidea) and its reproductive cycle in south-western Australia |journal = Marine Biology |year=2011 | bibcode = 2011MarBi.158.1163K | s2cid = 84926100}} and the male climbs on top, placing his arms between those of the female. When she releases eggs into the water, he is induced to spawn. 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. In some species, mature females produce chemicals to attract sperm in the sea water.{{Cite journal | doi = 10.1016/0022-0981(89)90164-0 | volume = 130 | issue = 3 | pages = 205–221| author = Miller, Richard L. | title = Evidence for the presence of sexual pheromones in free-spawning starfish | journal = Journal of Experimental Marine Biology and Ecology | date = 12 October 1989| bibcode = 1989JEMBE.130..205M }}

File:Haeckel Asteridea Larvae.jpg starfish larvae (from left to right) scaphularia larva, bipinnaria larva, brachiolaria larva, all of Asterias sp. Painted by Ernst Haeckel]]

Starfish embryos typically hatch as blastulas. Invaginations take place, the first creating the anus is created from blastopore, while a second, taking place in the ectodermic layer, creates the mouth. The archenteron stretches towards the mouth and connects with it, forming the gut.Ruppert et al., 2004. pp. 875 A band of cilia 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 a bipinnaria. The cilia are used for locomotion and feeding, their rhythmic beat wafting phytoplankton towards the mouth.

The next stage in development is a brachiolaria larva and involves the growth of three short ventral-anterior arms with adhesive tips and 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 the ventral arms and sucker. Metamorphosis now takes place with a radical rearrangement of tissues. The larvae develops an oral surface on the left and a aboral surface on the right. While the gut remains, the mouth and anus move to new positions. Some of the body cavities disappear but 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 {{convert|1|mm|2|abbr=on}} in diameter.

File:Tu - Linckia guildingi cropped.jpg, showing starfish body regrowing from a single arm]]

{{Main|Asexual reproduction in starfish}}

Some species of starfish can reproduce asexually as adults either by fission of their central discs or by autotomy of one or more of their arms.{{cite journal |author1=Achituv, Y. |author2=Sher, E. |year=1991 |title=Sexual reproduction and fission in the sea star Asterina burtoni from the Mediterranean coast of Israel |journal=Bulletin of Marine Science |volume=48 |issue=3 |pages=670–679 |url=http://www.ingentaconnect.com/content/umrsmas/bullmar/1991/00000048/00000003/art00007 }}{{cite journal |last1=Rubilar |first1=Tamara |last2=Pastor |first2=Catalina |last3=Diaz de Vivar |first3=Enriqueta |title=Timing of fission in the starfish Allostichaster capensis (Echinodermata:Asteroidea) in laboratory |journal=Revista de Biología Tropical |issue=53 (Supplement 3) |pages=299–303 |date=30 January 2006 |url=https://tropicalstudies.org/rbt/attachments/suppls/sup53-3%20echinoderm/20-RUBILAR-Tim.pdf}} Single arms that regenerate a whole individual are called comet forms.{{cite book|last=Dipper|first=Frances|year=2016|title=The Marine World: A Natural History of Ocean Life|publisher=Princeton University Press|page=291|isbn=978-0957394629}} The larvae of several species of starfish can reproduce asexually before they reach maturity.{{Cite journal |issn=0028-0836 |volume=425 |issue=6954|pages=146|author1=Eaves, Alexandra A. |author2=Palmer, A. Richard |title=Reproduction: widespread cloning in echinoderm larvae |journal=Nature |year=2003 |doi=10.1038/425146a |pmid=12968170|bibcode=2003Natur.425..146E |s2cid=4430104 |doi-access=free }} They do this by autotomising some parts of their bodies or by budding.{{Cite journal |doi=10.2307/1542036 |pmid=29283296 |volume=186 |issue=1 |pages=62–71 |last=Jaeckle |first=William B. |title=Multiple modes of asexual reproduction by tropical and subtropical sea star larvae: an unusual adaptation for genet dispersal and survival|journal=Biological Bulletin |year=1994 |jstor =1542036 |url=https://digitalcommons.iwu.edu/bio_scholarship/30 }} Larva increase asexual reproduction when senses that food is plentiful.{{Cite journal |volume=199 |issue=3 |pages=298–304 |author1=Vickery, M. S. |author2=McClintock, J. B. |title=Effects of food concentration and availability on the incidence of cloning in planktotrophic larvae of the sea star Pisaster ochraceus |journal=The Biological Bulletin |date=2000-12-01 |pmid=11147710 |doi=10.2307/1543186|jstor=1543186 |url=https://www.biodiversitylibrary.org/part/10580 }} 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.

{{Main|Starfish regeneration}}

File:Sea star regenerating legs.jpg regenerating missing arms]]

Some species of starfish have the ability to regenerate lost arms and can regrow an entire new limb given time. 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. Regrowth can take several months, and starfish are vulnerable to infections during the early stages after the loss of an arm.{{cite journal|last=Edmondson |first=C. H. |title=Autotomy and regeneration of Hawaiian starfishes |journal=Bishop Museum Occasional Papers |year=1935 |volume=11 |issue=8 |pages=3–20 |url=http://hbs.bishopmuseum.org/pubs-online/pdf/op11-8.pdf}} Other than fragmentation carried out for the purpose of reproduction, the division of the body may happen as a defense mechanism. 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. This type of tissue is called catch connective tissue and is found in most echinoderms.{{Cite journal| issn = 0022-0949| volume = 125| issue = 1| pages = 71–84|author1=Hayashi, Yutaka |author2=Motokawa, Tatsuo | title = Effects of ionic environment on viscosity of catch connective tissue in holothurian body wall| journal = Journal of Experimental Biology| year = 1986| doi = 10.1242/jeb.125.1.71| url =http://jeb.biologists.org/content/125/1/71.full.pdf+html | doi-access = free}} An autotomy-promoting factor has been identified which, when injected into another starfish, causes rapid shedding of arms.{{Cite journal| issn = 0006-3185| volume = 176| issue = 2| pages = 169–175| author1 = Mladenov, Philip V.| author2 = Igdoura, Suleiman| author3 = Asotra, Satish| author4 = Burke, Robert D.| title = Purification and partial characterization of an autotomy-promoting factor from the sea star Pycnopodia helianthoides| journal = Biological Bulletin| year = 1989| url = http://www.biolbull.org/content/176/2/169.full.pdf+html| doi = 10.2307/1541585| jstor = 1541585| access-date = 12 July 2013| archive-url = https://web.archive.org/web/20150923202150/http://www.biolbull.org/content/176/2/169.full.pdf+html| archive-date = 23 September 2015| url-status = dead}}

The lifespan of a starfish varies considerably between species. For example, Leptasterias hexactis at reaches sexual maturity at {{convert|20|g|1|abbr=on}} and in two years and lives for about ten years. Pisaster ochraceus matures at {{convert|70|–|90|g|abbr=on}}, and in five years and has a maximum recorded lifespan of 34 years.

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 species inhabit all of the world's oceans. Habitats range from tropical coral reefs, rocky shores, tidal pools, mud, and sand to kelp forests, seagrass meadows{{cite encyclopedia |url=http://www.encyclopedia.com/article-1G2-3406700053/asteroidea-sea-stars.html |title=Asteroidea (Sea Stars) |year=2004 |encyclopedia=Encyclopedia.com |publisher=Grzimek's Animal Life Encyclopedia |access-date=2012-07-14}} and the deep-sea floor down to at least {{convert|6000|m|abbr=on}}.{{cite journal |author1=Mah, Christopher |author2=Nizinski, Martha |author3=Lundsten, Lonny |year=2010 |title=Phylogenetic revision of the Hippasterinae (Goniasteridae; Asteroidea): systematics of deep sea corallivores, including one new genus and three new species |journal=Zoological Journal of the Linnean Society |volume=160 |issue=2 |pages=266–301 |doi=10.1111/j.1096-3642.2010.00638.x |doi-access=free }} The greatest diversity of species occurs in coastal areas.

File:Starfish eversion.jpg starfish everting its stomach to feed on coral]]

Most species are generalist predators, eating microalgae, sponges, bivalves, snails and other small animals. The crown-of-thorns starfish consumes coral polyps, while other species are detritivores, feeding on decomposing organic material and faecal matter.{{cite book |last=Pearse |first=J. S. |contribution=Odontaster validus |pages=124–25 |title=Starfish: Biology and Ecology of the Asteroidea|date=2014 |volume=10 |issue=1 |doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013){{cite book |last=Turner |first=R. L. |title=Starfish: Biology and Ecology of the Asteroidea |date=2014 |volume=10 |issue=1 |contribution=Echinaster |pages=206–207|doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2012) A few are suspension feeders, gathering in phytoplankton; Henricia and Echinaster often occur in association with sponges, benefiting from the water current they produce.{{cite book|author=Florkin, Marcel|title=Chemical Zoology V3: Echinnodermata, Nematoda, and Acanthocephala |url=https://books.google.com/books?id=43zXixxPk74C&pg=PA75 |year=2012 |publisher=Elsevier |isbn=978-0-323-14311-0 |pages=75–77}} 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.

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).{{cite book |title=Marine Biology: An Ecological Approach |last1=Nybakken |first1=James W. |last2=Bertness |first2=Mark D. |year=1997 |publisher=Addison-Wesley Educational Publishers |isbn=978-0-8053-4582-7 |page=174 }} 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. The gap between the valves need only be a fraction of a millimetre wide for the stomach to gain entry.{{cite book |title=Zoology |url=https://archive.org/details/zoology0000dori |url-access=registration |last1=Dorit |first1=R. L. |last2=Walker | first2= W. F. |last3=Barnes |first3 = R. D. |year=1991 |publisher=Saunders College Publishing |isbn=978-0-03-030504-7 |page=[https://archive.org/details/zoology0000dori/page/782 782] }} Cannibalism has been observed in juvenile sea stars as early as four days after metamorphosis.{{Cite web|title=Researcher reports cannibalistic echinoderm underwater dwellers|author=McClain, Joseph |date=5 April 2021|url=https://phys.org/news/2021-04-cannibalistic-echinoderm-underwater-dwellers.html |access-date=6 April 2021 |website=phys.org| language=en}}

File:Asteroidea bunch - 133 - 54001353478.jpg

Starfish are keystone species in their respective marine communities. Their relatively large sizes, diverse diets and ability to adapt to different environments makes them ecologically important.{{cite book |author1=Menage, B. A. |author2=Sanford, E. |title=Starfish: Biology and Ecology of the Asteroidea|date=2014 |volume=10 |issue=1 | contribution=Ecological Role of Sea Stars from Populations to Meta-ecosystems | page=67|doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013) The term "keystone species" was in fact first used by Robert Paine in 1966 to describe a starfish, Pisaster ochraceus.{{cite web | author=Wagner, S. C. | year=2012 | title=Keystone Species | publisher=Nature Education Knowledge | access-date=2013-05-16 | url=http://www.nature.com/scitable/knowledge/library/keystone-species-15786127}} 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. 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.{{cite journal | author=Paine, R. T. | year=1966 | title=Food web complexity and species diversity | journal=American Naturalist | volume=100 | issue=190 | pages=65–75 | jstor=2459379 | doi=10.1086/282400| s2cid=85265656 }} Similar results were found in a 1971 study of Stichaster australis on the intertidal coast of the South Island of New 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 which S. australis had been removed, the mussels increased in number dramatically, overwhelming the area and threatening biodiversity.{{cite journal | author=Paine, R. T. | year=1971 | title=A short-term experimental investigation of resource partitioning in a New Zealand rocky intertidal habitat | journal=Ecology | volume=52 | issue=6 | pages=1096–1106 | jstor=1933819 | doi=10.2307/1933819| bibcode=1971Ecol...52.1096P }}

File:Starfishmussel.jpg]]

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. These starfish engulf piles of sediment removing the surface films and algae adhering to the particles.{{cite journal |author=Wullf, L. |year=1995 |title=Sponge-feeding by the Caribbean starfish Oreaster reticulatus |journal=Marine Biology |volume=123 |issue=2 |pages=313–325 |doi=10.1007/BF00353623 |bibcode=1995MarBi.123..313W |s2cid=85726832 }} Organisms that dislike this disturbance are replaced by others better able to rapidly recolonise "clean" sediment. 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.{{cite journal|author=Scheibling, R. E. |year=1980 |title=Dynamics and feeding activity of high-density aggregations of Oreaster reticulatus (Echinodermata: Asteroidea) in a sand patch habitat |journal=Marine Ecology Progress Series |volume=2 |pages=321–27 |doi=10.3354/meps002321|bibcode=1980MEPS....2..321S |doi-access=free }}

Starfish sometimes have negative effects on ecosystems. Outbreaks of crown-of-thorns starfish have caused damage to coral reefs in Northeast Australia and French Polynesia.{{cite journal |author1=Kayal, Mohsen |author2=Vercelloni, Julie |author3=Lison de Loma, Thierry |author4=Bosserelle, Pauline |author5=Chancerelle, Yannick |author6=Geoffroy, Sylvie |author7=Stievenart, Céline |author8=Michonneau, François |author9=Penin, Lucie |author10=Planes, Serge |author11=Adjeroud, Mehdi | year=2012 | title=Predator crown-of-thorns starfish (Acanthaster planci) outbreak, mass mortality of corals, and cascading effects on reef fish and benthic communities|journal=PLOS ONE| volume=7 | issue=10 | page=e47363 | doi=10.1371/journal.pone.0047363 | editor1-last=Fulton | editor1-first=Christopher | pmid=23056635 | pmc=3466260|bibcode=2012PLoSO...747363K |doi-access=free }}{{cite journal |vauthors=Brodie J, Fabricius K, De'ath G, Okaji K |title=Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence |journal=Marine Pollution Bulletin |volume=51 |issue=1–4 |pages=266–78 |year=2005 |pmid=15757727 |doi=10.1016/j.marpolbul.2004.10.035|bibcode=2005MarPB..51..266B }} 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. This had a cascading effect on the whole benthic community and reef-feeding fish. Asterias amurensis is a rare example of an invasive echinoderm . Its larvae likely arrived in Tasmania from central Japan via water discharged from ships in the 1980s. The species has since grown in numbers to the point where they threaten important bivalves fisheries in Australia. As such, they are considered pests,{{cite book |author1=Byrne, M. |author2=O'Hara, T. D. |author3=Lawrence, J. M. | contribution=Asterias amurensis|title=Starfish: Biology and Ecology of the Asteroidea |date=2014 |volume=10 |issue=1 | pages=177–179|doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013) and are on the Invasive Species Specialist Group's list of the world's 100 worst invasive species.{{cite web|url=http://www.issg.org/database/species/search.asp?st=100ss|title=100 of the World's Worst Invasive Alien Species|publisher=Global Invasive Species Database|access-date=2010-07-16|archive-date=29 April 2015|archive-url=https://web.archive.org/web/20150429045453/http://www.issg.org/database/species/search.asp?st=100ss|url-status=dead}}

Sea Stars (starfish) are the main predators of kelp-eating sea urchins. Satellite imagery shows that sea urchin populations have exploded due to starfish mass deaths, and that by 2021, sea urchins have destroyed 95% of California's kelp forests.{{cite news|url=https://www.nytimes.com/2022/12/05/science/sea-cow-california-kelp.html?action=click&module=Well&pgtype=Homepage§ion=US%20News|title=The Missing Mammal (the extinct: Steller's sea cow) That May Have Shaped California's Kelp Forests|work=The New York Times |date=5 December 2022 |access-date=2022-12-05|last1=Whang |first1=Oliver }}

File:Seagull eating starfish.jpg feeding on a starfish]]

Starfish may be preyed on by conspecifics, sea anemones,{{cite web |title=Fact Sheet: Sea Anemones |url=https://www.mba.ac.uk/fact-sheet-sea-anemones |publisher=Marine Biological Association |access-date=10 June 2019 |date=21 February 2017 |archive-url=https://web.archive.org/web/20191224194037/https://www.mba.ac.uk/fact-sheet-sea-anemones |archive-date=24 December 2019 |url-status=dead }} other starfish species, tritons, crabs, fish, gulls and sea otters.{{cite book|title=Starfish: Biology and Ecology of the Asteroidea |author1=Gaymer, C. F. |author2=Himmelman, J. H. |date=2014 |volume=10 |issue=1 | contribution=Leptasterias polaris | pages=182–84|doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013){{cite book | author=Robles, C. | contribution=Pisaster ochraceus | pages=166–167|title=Starfish: Biology and Ecology of the Asteroidea| date=2014 | volume=10 | issue=1 | doi=10.1080/17451000.2013.820323 | bibcode=2014MBioR..10...93V }} in Lawrence (2013){{cite book| author=Scheibling, R. E. |contribution=Oreaster reticulatus|title=Starfish: Biology and Ecology of the Asteroidea |date=2014 |volume=10 |issue=1 |page=150|doi=10.1080/17451000.2013.820323 |bibcode=2014MBioR..10...93V }} in Lawrence (2013) Their first lines of defence are the saponins present in their body walls, which have unpleasant flavours. 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. They also have body armour in the form of hard plates and spines.{{cite web |url=http://echinoblog.blogspot.co.uk/2010/04/sea-star-defense-how-do-starfish.html |title=Sea star defense |author=Mah, Christopher |date=2010-04-20 |work=The Echinoblog |access-date=2013-05-30}} 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.{{cite web|url=http://sea.sheddaquarium.org/sea/fact_sheets.asp?id=69 |title=Crown of Thorns Sea Star |publisher=Shedd Aquarium |year=2006 |access-date=2013-05-22 |author=Shedd, John G. |url-status=dead |archive-url=https://web.archive.org/web/20140222070509/http://sea.sheddaquarium.org/sea/fact_sheets.asp?id=69 |archive-date=22 February 2014 }} Other species protect their vulnerable tube feet and arm tips by lining their ambulacral grooves with spines and heavily plating their extremities.

File:Crown of Thorns-jonhanson.jpg in the crown-of-thorns starfish]]

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. 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).{{cite journal | last1=Hewson | first1=Ian | last2=Button | first2=Jason B. | last3=Gudenkauf | first3=Brent M. | last4=Miner | first4=Benjamin | last5=Newton | first5=Alisa L. | last6=Gaydos | first6=Joseph K. | last7=Wynne | first7=Janna | last8=Groves | first8=Cathy L. | last9=Hendler | first9=Gordon| display-authors = 8 | year=2014 | title=Densovirus associated with sea-star wasting disease and mass mortality | journal=PNAS | doi=10.1073/pnas.1416625111 | volume=111 | issue=48 | pages=17278–17283 | pmid=25404293 | pmc=4260605| bibcode=2014PNAS..11117278H | doi-access=free }}

The results of a study published in 2025 suggest that lower temperatures and higher salinity in fjords off the coast of central British Columbia are providing refuges for populations of sea stars affected by the virus.{{Cite web |author=Nono Shen|agency=The Canadian Press |date=2025-04-02 |title=Critically endangered sunflower sea stars are seeking refuge in B.C. fiords |url=https://www.thecanadianpressnews.ca/national/critically-endangered-sunflower-sea-stars-are-seeking-refuge-in-b-c-fiords/article_2d1b3c80-3dbe-56f8-b955-d49b6fc8e458.html |access-date=2025-04-09 |website=thecanadianpressnews.ca |language=en}}{{Cite journal |last=Gehman |first=Alyssa-Lois Madden |last2=Pontier |first2=Ondine |last3=Froese |first3=Tyrel |last4=VanMaanen |first4=Derek |last5=Blaine |first5=Tristan |last6=Sadlier-Brown |first6=Gillian |last7=Olson |first7=Angeleen M. |last8=Monteith |first8=Zachary L. |last9=Bachen |first9=Krystal |last10=Prentice |first10=Carolyn |last11=Hessing-Lewis |first11=Margot |last12=Jackson |first12=Jennifer M. |date=2025-04-02 |title=Fjord oceanographic dynamics provide refuge for critically endangered Pycnopodia helianthoides |url=https://royalsocietypublishing.org/doi/10.1098/rspb.2024.2770 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=292 |issue=2044 |pages=20242770 |doi=10.1098/rspb.2024.2770 |pmc=11961252 |pmid=40169020}} The protozoan Orchitophrya stellarum is known to infect and damage the gonads of starfish. Starfish are vulnerable to high temperatures. Experiments have shown that the feeding and growth rates of P. ochraceus reduce greatly when their body temperatures rise above {{convert|23|C|F|0|abbr=on}} and that they die when their temperature rises to {{convert|30|C|F|0|abbr=on}}.{{cite journal |author1=Peters, L. E. |author2=Mouchka M. E. |author3=Milston-Clements, R. H. |author4=Momoda, T. S. |author5=Menge, B. A. |year=2008 |title=Effects of environmental stress on intertidal mussels and their sea star predators |journal=Oecologia |volume=156 |issue=3 |pages=671–680 |doi=10.1007/s00442-008-1018-x |pmid=18347815|bibcode=2008Oecol.156..671P |s2cid=19557104 }}{{cite journal|author1=Pincebourde, S. |author2=Sanford, E. |author3=Helmuth, B. |year=2008 |title=Body temperature during low tide alters the feeding performance of a top intertidal predator |journal=Limnology and Oceanography |volume=53 |issue=4 |pages=1562–1573|doi= 10.4319/lo.2008.53.4.1562|bibcode=2008LimOc..53.1562P |s2cid=1043536 |doi-access=free }} This species has a unique ability to absorb seawater to keep itself cool when it is exposed to sunlight by a receding tide.{{cite journal|author1=Pincebourde, S. |author2=Sanford, E. |author3=Helmuth, B. |year=2009 |title=An intertidal sea star adjusts thermal inertia to avoid extreme body temperatures |journal=The American Naturalist |volume=174 |issue=6 |pages=890–897 |jstor=10.1086/648065|doi=10.1086/648065|pmid=19827942|s2cid=13862880 |url=https://scholarcommons.sc.edu/biol_facpub/54 |url-access=subscription }} It also appears to rely on its arms to absorb heat, so as to protect the central disc and vital organs like the stomach.{{cite journal|author1=Pincebourde, S. |author2=Sanford, E. |author3=Helmuth, B. |year=2013|title=Survival and arm abscission are linked to regional heterothermy in an intertidal sea star|journal=Journal of Experimental Biology|volume=216|issue=12|pages=2183–2191|doi=10.1242/jeb.083881 |pmid=23720798|s2cid=4514808 |doi-access=free}}

Starfish and other echinoderms are sensitive to marine pollution.{{cite journal|author1=Newton, L. C. |author2=McKenzie, J. D. |year=1995|title=Echinoderms and oil pollution: A potential stress assay using bacterial symbionts |journal=Marine Pollution Bulletin|volume=31 |issue=4–12|pages=453–456 |doi=10.1016/0025-326X(95)00168-M|bibcode=1995MarPB..31..453N }} The common starfish is considered to be a bioindicator for marine ecosystems.{{cite journal|author1=Temara, A. |author2=Skei, J.M. |author3=Gillan, D. |author4=Warnau, M. |author5=Jangoux, M. |author6=Dubois, Ph. |year=1998|title=Validation of the asteroid Asterias rubens (Echinodermata) as a bioindicator of spatial and temporal trends of Pb, Cd, and Zn contamination in the field|journal=Marine Environmental Research|volume=45|issue=4–5 |pages=341–56 |doi=10.1016/S0141-1136(98)00026-9|bibcode=1998MarER..45..341T }} A 2009 study found that P. ochraceus is unlikely to be affected by ocean acidification as severely as other marine animals with calcareous skeletons. In other groups, structures made of calcium carbonate are vulnerable to dissolution when the pH is lowered. Researchers found that when P. ochraceus were exposed to {{convert|21|C|F}} and 770 ppm carbon 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.{{cite journal |last1=Gooding|last2= Harley|last3= Tang|year=2009 |title=Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm|journal=Proceedings of the National Academy of Sciences |volume=106 |issue=23 |pages=9316–9321 |doi=10.1073/pnas.0811143106 |pmid=19470464 |pmc=2695056 |first1=Rebecca A. |first2= Christopher D. G. |first3=Emily |bibcode= 2009PNAS..106.9316G|doi-access= free}}

File:Riedaster reicheli.JPG, from the Plattenkalk Upper Jurassic limestone, Solnhofen]]

File:Zichor asteroid oral surface.jpg; Zichor Formation (Coniacian, Upper Cretaceous), southern Israel.]]

Echinoderms first appeared in the fossil record in the Cambrian. The first known asterozoans were the Somasteroidea, which exhibit characteristics of both groups.{{cite web |url=http://www.ucmp.berkeley.edu/echinodermata/echinofr.html |title=Echinodermata: Fossil Record |author=Wagonner, Ben |year=1994 |work=Echinodermata |publisher=The Museum of Paleontology of The University of California at Berkeley |access-date=2013-05-31}} 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 in Lagerstätten – so-called "starfish beds".{{cite book |title=Introduction to Paleobiology and the Fossil Record |last1=Benton |first1=Michael J. |author-link = Michael Benton|last2=Harper |first2=David A. T. |author-link2 = David Harper (palaeontologist)|year=2013 |publisher=Wiley |chapter=15. Echinoderms |isbn=978-1-118-68540-2 |chapter-url=https://books.google.com/books?id=ZQ1U9wmoensC&q=%22Starfish+bed%22+fossil&pg=PT691 }}

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. 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. 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.{{cite journal |author1=Mah, Christopher L. |author2=Blake, Daniel B. |year=2012 |title=Global diversity and phylogeny of the Asteroidea (Echinodermata) |journal=PLOS ONE|volume=7 |issue=4 |pages=e35644 |doi=10.1371/journal.pone.0035644 |pmid=22563389 |pmc=3338738 |bibcode=2012PLoSO...735644M |editor1-last=Badger |editor1-first=Jonathan H|doi-access=free }} A 2012 study found that speciation in starfish can occur rapidly. 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.{{cite journal|author1=Purit, J. B. |author2=Keever, C. C. |author3=Addison, J. A. |author4=Byrne, M. |author5=Hart, M. W. |author6=Grosberg, R. K. |author7=Toonen, R. J. |year=2012|title=Extraordinarily rapid life-history divergence between Cryptasterina sea star species|journal=Proceedings of the Royal Society B: Biological Sciences |volume=279 |issue=1744 |pages=3914–3922 |doi=10.1098/rspb.2012.1343 |pmid=22810427 |pmc=3427584}}

{{see also|List of echinodermata orders}}

File:Seastar.webm

File:Peppermint sea star, treasure chest, wakatobi, 2018 (31942194528).jpg, 2018]]

The scientific name Asteroidea was given to starfish by the French zoologist de Blainville in 1830.{{cite WoRMS |author=Hansson, Hans |year=2013 |title=Asteroidea |id=123080 |access-date=2013-07-19 }} It is derived from the Greek aster, ἀστήρ (a star) and the Greek eidos, εἶδος (form, likeness, appearance).{{cite web |url=http://www.myetymology.com/latin/Asteroidea.html |archive-url=https://web.archive.org/web/20131021164652/http://www.myetymology.com/latin/Asteroidea.html |url-status=usurped |archive-date=21 October 2013 |title=Etymology of the Latin word Asteroidea |year=2008 |work=MyEtymology |access-date=2013-07-19}} The class Asteroidea belongs to the phylum Echinodermata. As well as the starfish, the echinoderms include sea urchins, sand dollars, brittle and basket stars, sea cucumbers and crinoids. The larvae of echinoderms have bilateral symmetry, but during metamorphosis this is replaced with radial symmetry, typically pentameric.{{cite web |url=http://lanwebs.lander.edu/faculty/rsfox/invertebrates/asterias.html |title=Asterias forbesi |author= Fox, Richard |date=2007-05-25 |work=Invertebrate Anatomy OnLine |publisher=Lander University |access-date=2012-05-19}} 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.{{cite web |url=http://tolweb.org/Echinodermata/2497 |title=Echinodermata: Spiny-skinned animals: sea urchins, starfish, and their allies |author=Wray, Gregory A. |year=1999 |work=Tree of Life web project |access-date=2012-10-19}} 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. The subphylum includes the two classes of Asteroidea, the starfish, and Ophiuroidea, the brittle stars and basket stars. Asteroids have broad-based arms with skeletal support provided by calcareous plates in the body wall{{cite web |url=http://tolweb.org/Asteroidea |title=Asteroidea: Sea stars and starfishes |author=Knott, Emily |year=2004 |work=Tree of Life web project |access-date=2012-10-19}} while ophiuroids have clearly demarcated slender arms strengthened by paired fused ossicles forming jointed "vertebrae".{{cite web |url=http://www.marinespecies.org/ophiuroidea/ |title=World Ophiuroidea Database |author1=Stöhr, S. |author2=O'Hara, T. |access-date=2012-10-19}}

The starfish are a large and diverse class with over 1,900 living species. There are seven extant orders, Brisingida, Forcipulatida, Notomyotida, Paxillosida, Spinulosida, Valvatida and Velatida and two extinct ones, Calliasterellidae and Trichasteropsida. Living asteroids, the Neoasteroidea, are morphologically distinct from their forerunners in the Paleozoic. 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. 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.

File:Manningstar 600.jpg]]

; Brisingida (2 families, 17 genera, 111 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Brisingida |id=123085 |access-date=2012-09-15 |db=World Asteroidea}}

: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.{{cite journal |url=http://si-pddr.si.edu/dspace/bitstream/10088/5505/2/SCtZ-0435-Lo_res.pdf |title=Revision of the Atlantic Brisingida (Echinodermata: Asteroidea), with description of a new genus and family |author=Downey, Maureen E. |year=1986 |journal=Smithsonian Contributions to Zoology |issue=435 |pages=1–57 |publisher=Smithsonian Institution Press |doi=10.5479/si.00810282.435 |access-date=2012-10-18 |archive-date=27 February 2012 |archive-url=https://web.archive.org/web/20120227010606/http://si-pddr.si.edu/dspace/bitstream/10088/5505/2/SCtZ-0435-Lo_res.pdf |url-status=dead }}{{cite encyclopedia |url=http://accessscience.com/abstract.aspx?id=900559 |title=Brisingida |encyclopedia=Access Science: Encyclopedia |publisher=McGraw-Hill |author=Mah, Christopher |access-date=2012-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20121030063248/http://accessscience.com/abstract.aspx?id=900559 |archive-date=30 October 2012}} In some species, the tube feet have rounded tips and lack suckers.{{cite journal |author1=Vickery, Minako S. |author2=McClintock, James B. |year=2000 |title=Comparative morphology of tube feet among the Asteroidea: phylogenetic implications |journal=Integrative and Comparative Biology |volume=40 |issue=3 |pages=355–364 |doi=10.1093/icb/40.3.355 |doi-access=free }}

File:Starfish, Caswell Bay - geograph.org.uk - 409413.jpg, a member of Forcipulatida]]

; Forcipulatida (6 families, 63 genera, 269 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Forcipulatida |id=123086 |access-date=2012-09-15 |db=World Asteroidea}}

:Species in this order have distinctive pedicellariae, consisting of a short stalk with three skeletal ossicles. They tend to have robust bodies{{cite book |author=Barnes, Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |page= 948 |isbn=978-0-03-056747-6}} 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.{{cite encyclopedia |url=http://accessscience.com/abstract.aspx?id=900558&referURL=http%3a%2f%2faccessscience.com%2fcontent.aspx%3fsearchStr%3dForcipulatida%26id%3d900558 |title=Forcipulatida |author=Mah, Christopher |encyclopedia=Access Science: Encyclopedia |publisher=McGraw-Hill |access-date=2012-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20121030063255/http://accessscience.com/abstract.aspx?id=900558&referURL=http%3A%2F%2Faccessscience.com%2Fcontent.aspx%3FsearchStr%3DForcipulatida%26id%3D900558 |archive-date=30 October 2012}}

; Notomyotida (1 family, 8 genera, 75 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Notomyotida |id=123087 |access-date=2012-09-15 |db=World Asteroidea}}

: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.

File:Luidia magnifica mouth.jpg, a member of Paxillosida]]

; Paxillosida (7 families, 48 genera, 372 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Paxillosida |id=123088 |access-date=2012-09-15 |db=World Asteroidea}}

: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 present on their aboral surface and they possess marginal plates and paxillae. They mostly inhabit soft substrates.Ruppert et al, 2004. pp. 887–889 There is no brachiolaria stage in their larval development.{{cite journal |author1=Matsubara, M. |author2=Komatsu, M. |author3=Araki, T. |author4=Asakawa, S. |author5=Yokobori, S.-I. |author6=Watanabe, K. |author7=Wada, H. |year=2005 |title=The phylogenetic status of Paxillosida (Asteroidea) based on complete mitochondrial DNA sequences |journal=Molecular Genetics and Evolution |volume=36 |issue=3 |pages=598–605 |doi=10.1016/j.ympev.2005.03.018 |pmid=15878829 |bibcode=2005MolPE..36..598M }} The comb starfish (Astropecten polyacanthus) is a member of this order.{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Astropecten polyacanthus Müller & Troschel, 1842 |id=213245 |access-date=2013-07-06 |db=World Asteroidea}}

File:Estrella de mar de espinas rojas (Protoreaster linckii), Zanzíbar, Tanzania, 2024-06-01, DD 06.jpg, a member of Valvatida]]

; Spinulosida (1 family, 8 genera, 121 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Spinulosida |id=123089 |access-date=2012-09-15 |db=World Asteroidea}}

: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.{{cite encyclopedia |url=http://accessscience.com/overflow.aspx?SearchInputText=Spinulosida+&ContentTypeSelect=4 |title=Spinulosida |encyclopedia=Access Science: Encyclopedia |publisher=McGraw-Hill |access-date=2012-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20121030063309/http://accessscience.com/overflow.aspx?SearchInputText=Spinulosida+&ContentTypeSelect=4 |archive-date=30 October 2012}} This group includes the red starfish Echinaster sepositus.{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Echinaster (Echinaster) sepositus (Retzius, 1783) |id=125161 |access-date=2013-07-06 |db=World Asteroidea}}

; Valvatida (16 families, 172 genera, 695 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Valvatida |id=123090 |access-date=2012-09-15 |db=World Asteroidea}}

: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.{{cite journal |author=Blake, Daniel B. |year=1981 |title=A reassessment of the sea-star orders Valvatida and Spinulosida |journal=Journal of Natural History |volume=15 |issue=3 |pages=375–394 |doi=10.1080/00222938100770291 |bibcode=1981JNatH..15..375B }} This group includes the cushion stars,{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Culcita (Agassiz, 1836) |id=204844 |access-date=2013-07-06 |db=World Asteroidea}} the leather star{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Dermasterias imbricata (Grube, 1857) |id=240771 |access-date=2013-07-06 |db=World Asteroidea}} and the sea daisies.{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Xyloplax Baker, Rowe & Clark, 1986 |id=254802 |access-date=2013-07-06 |db=World Asteroidea}}

; Velatida (4 families, 16 genera, 138 species){{cite WoRMS |author=Mah, Christopher |year=2012 |title=Velatida |id=123091 |access-date=2012-09-15 |db=World Asteroidea}}

: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.{{cite encyclopedia |url=http://accessscience.com/abstract.aspx?id=900662&referURL=http%3a%2f%2faccessscience.com%2fcontent.aspx%3fid%3d900662 |title=Velatida |author=Mah, Christopher |encyclopedia=Access Science: Encyclopedia |publisher=McGraw-Hill |access-date=2012-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20121030063303/http://accessscience.com/abstract.aspx?id=900662&referURL=http%3A%2F%2Faccessscience.com%2Fcontent.aspx%3Fid%3D900662 |archive-date=30 October 2012}} This group includes the slime star.{{cite WoRMS |author=Mah, Christopher |year=2012 |title=Pteraster tesselatus Ives, 1888 |id=369053 |access-date=2013-07-06 |db=World Asteroidea}}

Extinct groups within the Asteroidea include:{{cite web | url=http://tolweb.org/Asteroidea | title=Asteroidea. Sea stars and starfishes | publisher=Tree of Life web project| date=7 October 2004| access-date=2013-05-10 | author=Knott, Emily}}

• † Calliasterellidae, with the type genus Calliasterella from the Devonian and Carboniferous{{cite web | url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=101372 | title=Family Calliasterellidae | publisher=Paleobiology Database | access-date=2013-05-10 | archive-date=9 March 2016 | archive-url=https://web.archive.org/web/20160309101759/http://paleodb.org/?a=basictaxoninfo&taxon_no=101372 | url-status=live }}
• † Palastericus, a Devonian genusWalker, Cyril, Ward, DavidFossils : Smithsonian Handbook, {{ISBN|0-7894-8984-8}} (2002, paperback, revisited), {{ISBN|1-56458-074-1}} (1992, 1st edition). Page 186
• † Trichasteropsida, with the Triassic genus Trichasteropsis (at least 2 species)

Starfish are deuterostome animals, like the chordates. A 2014 analysis of 219 genes from all classes of echinoderms gives the following phylogenetic tree.{{cite journal |last1=Telford |first1=M. J. |last2=Lowe|first2=C. J.|last3=Cameron |first3=C. B. |last4=Ortega-Martinez |first4=O. |last5=Aronowicz |first5=J. |last6=Oliveri|first6=P. |last7=Copley |first7=R. R. |title=Phylogenomic analysis of echinoderm class relationships supports Asterozoa |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1786 |year=2014 |pages=20140479 |doi=10.1098/rspb.2014.0479|pmid=24850925 |pmc=4046411 }} The times at which the clades diverged are shown under the labels in millions of years ago (mya).

{{Clade

|label1=Bilateria

|1={{Clade

|1=Xenacoelomorpha 80 px

|label2=Nephrozoa |sublabel2=650 mya

|2={{clade

|label1=Deuterostomia |sublabel1=>540 mya

|1={{clade

|1=Chordata 80 px

|label2=Echinodermata |sublabel2=c. 500 mya

|2={{clade

|label1=Eleutherozoa

|1={{clade

|label1=Echinozoa

|1={{clade

|1=Holothuroidea 80 px

|2=Echinoidea 80 px

}}

|label2=Asterozoa

|2={{clade

|1=Ophiuroidea 80 px

|2=Asteroidea 100 px

}}

}}

|2=Crinoidea 50 px

}}

}}

|label2 =Protostomia |sublabel2=610 mya

|2={{Clade

|1=Ecdysozoa 80 px

|2=Spiralia 80 px

}}

}}

}}

}}

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. The phylogeny proposed by Gale in 1987 is:{{cite journal | title=Phylogeny and classification of the Asteroidea (Echinodermata) | author=Gale, A. S. | journal=Zoological Journal of the Linnean Society | year=1987 | volume=89 | pages=107–132 | doi=10.1111/j.1096-3642.1987.tb00652.x | issue=2}}

{{clade | style = font-size: 90%; line-height:75%

|1={{clade

|1=† Palaeozoic Asteroids

|2={{clade

|1={{clade

|1=Paxillosida

|2={{clade

|1=Valvatida, including Velatida, Spinulosida (not a clade)

|2=Forcipulatida, including Brisingida

}}

}}

}}

}}

}}

The phylogeny proposed by Blake in 1987 is:{{cite journal | title=A classification and phylogeny of post-Paleozoic sea stars (Asteroidea: Echinodermata) | author=Blake, D. B. | journal=Journal of Natural History | year=1987 | volume=21 | pages=481–528 | doi=10.1080/00222938700771141 | issue=2| bibcode=1987JNatH..21..481B }}

{{clade | style = font-size: 90%; line-height:75%

|1={{clade

|1=† Palaeozoic Asteroids

|2={{clade

|1={{clade

|1=† Calliasterellidae

|2={{clade

|1=† Compasteridae

|2={{clade

|1=† Trichasteropsida

|2={{clade

|1={{clade

|1=Brisingida

|2=Forcipulatida

}}

|2={{clade

|1={{clade

|1=Spinulosida

|2=Velatida

}}

|2={{clade

|1={{clade

|1=Notomyotida

|2=Valvatida

}}

|2=Paxillosida

}}

}}

}}

}}

}}

}}

}}

}}

}}

Later work making use of molecular evidence, with or without the use of morphological evidence, had by 2000 failed to resolve the argument. 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.{{cite journal | title=Echinoderm phylogeny including Xyloplax, a progenetic asteroid |author1=Janies, Daniel A. |author2=Voight, Janet R. |author3=Daly, Marymegan | journal=Syst. Biol. | year=2011 | volume=60 | issue=4 | pages=420–438 | doi=10.1093/sysbio/syr044 | pmid=21525529| doi-access=free }}

{{clade | style = font-size: 85%; line-height:75%

|1={{clade

|1={{clade

|1={{clade

|1={{clade

|1={{clade

|1={{clade

|1=Solasteridae and part of Spinulosida, e.g. Stegnaster and part of Valvatida, e.g. Asterina

|2=Odontasteridae, which was a part of Valvatida

}}

|2=Paxillosida

}}

|2=part of Spinulosida, e.g. Echinaster, part of Valvatida, e.g. Archaster

}}

|2={{clade

|1=Forcipulatida

|2=Brisingida with part of Velatida, e.g. Caymanostella and part of Forcipulatida, e.g. Stichaster

}}

}}

}}

|2= Velatida except for Solasteridae

}}

}}

{{clade | style = font-size: 90%; line-height:75%

|1=Notomyotida (not analysed)

}}

File:CalcifiedStarfish.jpg]]

Starfish are deuterostomes, closely related, together with all other echinoderms, to chordates, and are used in reproductive and developmental studies. 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.{{cite journal |author1=Wessel, G. M. |author2=Reich, A. M. |author3=Klatsky, P. C. |year=2010 |title=Use of sea stars to study basic reproductive processes |journal=Systems Biology in Reproductive Medicine |volume=56 |issue=3 |pages=236–245 |doi=10.3109/19396361003674879 |pmid=20536323 |pmc=3983664}} 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.{{cite web |url=http://www.embl.de/research/units/cbb/lenart/ |title=Cytoskeletal dynamics and function in oocytes |author=Lenart Group |publisher=European Molecular Biology Laboratory |access-date=2013-07-22 |archive-url=https://web.archive.org/web/20140801190144/http://www.embl.de/research/units/cbb/lenart/ |archive-date=1 August 2014 |url-status=dead}} Asterina pectinifera, used as a model organism for this purpose, is resilient and easy to breed and maintain in the laboratory.{{cite book |title=Animal Species for Developmental Studies: The Starfish Asterina pectinifera |last1=Davydov |first1=P. V. |last2=Shubravyi |first2=O. I. |last3=Vassetzky |first3=S. G. |year=1990 |publisher=Springer US |isbn=978-1-4612-7839-9 |doi=10.1007/978-1-4613-0503-3 |pages=287–311 |s2cid=42046815 }}

Another area of research is the ability of starfish to regenerate lost body parts. 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.{{cite journal |author1=Friedman, Rachel S. C. |author2=Krause, Diane S. |year=2009 |title=Regeneration and repair: new findings in stem cell research and ageing |journal=Annals of the New York Academy of Sciences |volume=1172 |issue=1 |pages=88–94 |doi=10.1111/j.1749-6632.2009.04411.x |pmid=19735242 |s2cid=755324 }}

Starfish also have an unusual ability to expel foreign objects from their bodies, which makes them difficult to tag for research tracking purposes.{{cite web |url=http://www.techtimes.com/articles/61562/20150619/starfish-shows-off-strange-ability-to-expel-foreign-objects-through-skin.htm |title=Starfish Shows Off Strange Ability To Expel Foreign Objects Through Skin |newspaper=Tech Times, Science |author=Ted Ranosa |date= 19 June 2015 |url-status=live |archive-url=https://web.archive.org/web/20160101005129/http://www.techtimes.com/articles/61562/20150619/starfish-shows-off-strange-ability-to-expel-foreign-objects-through-skin.htm |archive-date=2016-01-01}}

File:Poems of the Sea, 1850 - Hope in God.png

An aboriginal Australian fable retold by the Welsh school headmaster William Jenkyn Thomas (1870–1959){{cite web | url=http://www.abgs.org.uk/teachers/headmasters/wjt/wjt.htm | title=William Jenkyn Thomas, M.A | publisher=The Aberdare Boys' Grammar School | access-date=2013-05-12 | archive-date=6 June 2014 | archive-url=https://web.archive.org/web/20140606204726/http://www.abgs.org.uk/teachers/headmasters/wjt/wjt.htm | url-status=dead }} 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.{{cite book | url=http://www.sacred-texts.com/aus/mla/mla08.htm | title=Some Myths and Legends of the Australian Aborigines | publisher=Whitcombe & Tombs | author=Thomas, William Jenkyn | year=1943 | pages=21–28}}

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. Among the "uncreated gods" described early in the song are the male Kumulipo ("Creation") and the female Poele, both born in the night, a coral insect, the earthworm, and the starfish.{{cite journal | url=http://www.jps.auckland.ac.nz/document/Volume_9_1900/Volume_9,_No._1,_March_1900/%26%2339%3BThe_creation_song%26%2339%3B_of_Hawaii,_by_Edward_Tregear,_p_38-46/p1 | title="The Creation Song" of Hawaii | author=Tregear, Edward | journal=The Journal of the Polynesian Society | year=1900 | volume=9 | issue=1 | pages=38–46 | author-link=Edward Robert Tregear | access-date=13 May 2013 | archive-date=12 February 2016 | archive-url=https://web.archive.org/web/20160212145154/http://www.jps.auckland.ac.nz/document//Volume_9_1900/Volume_9%2C_No._1%2C_March_1900/%26%2339%3BThe_creation_song%26%2339%3B_of_Hawaii%2C_by_Edward_Tregear%2C_p_38-46/p1 | url-status=dead }}

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. 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".{{cite book | title=The Ambonese Curiosity Cabinet (original title: Amboinsche Rariteitkamer) | publisher=Yale University Press | author=Rumphius, Georgious Everhardus (= Georg Eberhard Rumpf); Beekman, E.M. (trans.) | year=1999|orig-year=1705 | isbn=978-0-300-07534-2 | page=68}}

File:What to eat - strange food in China.jpg

Starfish are widespread in the oceans, but are only occasionally used as food. 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,{{cite journal |author=Andersson L, Bohlin L, Iorizzi M, Riccio R, Minale L, Moreno-López W |title=Biological activity of saponins and saponin-like compounds from starfish and brittle-stars |journal=Toxicon |volume=27 |issue=2 |pages=179–88 |year=1989 |pmid=2718189 |doi=10.1016/0041-0101(89)90131-1 |last2=Bohlin |last3=Iorizzi |last4=Riccio |last5=Minale |last6=Moreno-López |bibcode=1989Txcn...27..179A }} and others contain tetrodotoxins which are poisonous.{{cite journal |author=Lin SJ, Hwang DF |title=Possible source of tetrodotoxin in the starfish Astropecten scoparius |journal=Toxicon |volume=39 |issue=4 |pages=573–9 |date=April 2001 |pmid=11024497 |doi=10.1016/S0041-0101(00)00171-9 |last2=Hwang |bibcode=2001Txcn...39..573L }} Some species that prey on bivalve molluscs can transmit paralytic shellfish poisoning.{{cite journal | title=Occurrence of paralytic shellfish poison in the starfish Asterias amurensis in Kure Bay, Hiroshima Prefecture, Japan | year=1997 |author1=Asakawa, M. |author2=Nishimura, F. |author3=Miyazawa, K. |author4=Noguchi, T. | journal=Toxicon | volume=35 | issue=7 | pages=1081–1087 | doi=10.1016/S0041-0101(96)00216-4 | pmid=9248006| bibcode=1997Txcn...35.1081A }} 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 are sometimes eaten in China,{{cite web | url=http://www.thechinaguide.com/food/exotic.html | title=Indulging in Exotic Cuisine in Beijing | publisher=The China Guide | date=2011 | access-date=28 February 2014 | url-status=dead | archive-url=https://web.archive.org/web/20140303173324/http://www.thechinaguide.com/food/exotic.html | archive-date=3 March 2014}} Japan{{cite web | url=http://www.amakusa.tv/enewshito.html#ibook | title=Cooking Starfish in Japan | publisher=Amakusa TV | work=ebook10005 | date=2011-08-07 | access-date=2013-05-18 | author=Amakusa TV Co. Ltd.}}{{cite web | url=http://search.kenko.com/product/%E5%B0%8F%E8%A2%8B | title=Pouch A | language=ja | publisher=Kenko.com | access-date=2013-05-18 | url-status=dead | archive-url=https://web.archive.org/web/20140803035529/http://search.kenko.com/product/%E5%B0%8F%E8%A2%8B | archive-date=3 August 2014}} and in Micronesia.{{cite book | title=Words of the Lagoon: Fishing and Marine Lore in the Palau District of Micronesia | url=https://archive.org/details/bub_gb_TloVDfV7QLoC | publisher=University of California Press | author=Johannes, Robert Earle | year=1981 | pages=[https://archive.org/details/bub_gb_TloVDfV7QLoC/page/n100 87]}}

Starfish are in some cases taken from their habitat and sold to tourists as souvenirs, 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 the State of Florida, O. reticulatus is listed as endangered and its collection is illegal. Nevertheless, it is still sold both in and outside its range. A similar phenomenon exists in the Indo-Pacific for species such as Protoreaster nodosus.{{cite journal |author1=Bos, A. R. |author2=Gumanao, G. S. |author3=Alipoyo, J. C. E. |author4=Cardona, L. T. |year=2008 |title=Population dynamics, reproduction and growth of the Indo-Pacific horned sea star, Protoreaster nodosus (Echinodermata; Asteroidea)|journal=Marine Biology |volume=156 |issue=1 |pages=55–63 |url=https://www.researchgate.net/publication/230887109 |doi=10.1007/s00227-008-1064-2|s2cid=84521816 |doi-access=free |bibcode=2008MarBi.156...55B |hdl=2066/72067 |hdl-access=free }}

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• {{cite book | editor=Lawrence, J. M. | year=2013 | title=Starfish: Biology and Ecology of the Asteroidea | publisher=Johns Hopkins University Press | isbn=978-1-4214-0787-6}}
• {{cite book | last1=Ruppert | first1=Edward E. | last2=Fox | first2=Richard S. | last3=Barnes | first3=Robert D. | year=2004 | title=Invertebrate Zoology |edition=7th | publisher=Cengage Learning | isbn=978-81-315-0104-7}}

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{{Commons|Starfish}}

• {{cite web |last1=Mah |first1=Christopher L. |date=24 January 2012 |title=The Echinoblog |url=http://echinoblog.blogspot.fr/2012/01/how-to-tell-apart-knobby-stars.html}} A blog about sea stars by a passionate and professional specialist.

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