Starfish 228613 226124297 2008-07-16T22:39:24Z SchfiftyThree 556700 Reverted edits by [[Special:Contributions/24.230.37.79|24.230.37.79]] to last version by Jumbuck (using [[WP:HG|Huggle]]) {{Taxobox | name = Sea Star | image = Haeckel Asteridea.jpg | image_width = 240px | image_caption = "Asteroidea" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904 | regnum = [[Animal]]ia | phylum = [[Echinodermata]] | subphylum = [[Asterozoa]] | classis = '''Asteroidea''' | subdivision_ranks = [[Order (biology)|Orders]] | subdivision = [[Brisingida]] (100 species<ref name="Asterozoa"> {{cite web|url=http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/asteroz2/index_f/mod_fm.html |title=Asterozoa: Fossil groups: SciComms 05-06: Earth Sciences |accessdate=2008-05-07 |last=Sweet |first=Elizabeth |date=2005-11-22 }}</ref>)<br> [[Forcipulatida]] (300 species<ref name="Asterozoa" />)<br> [[Paxillosida]] (255 species<ref name="Asterozoa" />)<br> [[Notomyotida]] (75 species<ref name="Asterozoa" />)<br> [[Spinulosida]] (120 species<ref name="Asterozoa" />)<br> [[Valvatida]] (695 species<ref name="Asterozoa" />)<br> [[Velatida]] (200 species<ref name="Asterozoa" />) }} {{otheruses}} '''Starfish''' (also called '''sea stars''') are any [[echinoderm]]s belonging to the [[class (biology)|class]] '''Asteroidea'''. The names "sea star" and "starfish" are also used in a broader sense to include the closely related [[brittle star]]s, which make up the class [[Ophiuroidea]]. Starfish exhibit a superficially [[symmetry (biology)#Radial symmetry|radial symmetry]]. They typically have five or more "arms" which radiate from an indistinct disk ([[symmetry (biology)#Pentamerism|pentaradial symmetry]]). However, the evolutionary ancestors of echinoderms are believed to have had [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]]. Starfish do exhibit some superficial remnant of this body structure, evident in their larval pluteus forms. Starfish do not rely on a jointed, movable [[skeleton]] for support and locomotion (although they are protected by their skeleton), but instead possess a hydraulic [[water vascular system]] that aids in locomotion. The water vascular system has many projections called [[tube feet]] on the [[ventral]] face of the starfish's arms which function in [[Animal locomotion|locomotion]] and aid with [[feeding]]. The star fish usually hunt for shelled animals such as oysters and clams. They have two stomachs. One stomach is used for digestion, and the other stomach can be extended outward to engulf and digest prey. This feature allows the starfish to hunt prey that is much larger than its mouth would otherwise allow. Starfish are able to regenerate lost arms. A new starfish may be regenerated from a single arm attached to a portion of the central disk. ==External anatomy== [[Image:Schmedelian pin-cushion sea star.jpg|thumb|left|200px|Schmedelian pin-cushion sea star on [[Meedhupparu]] house reef in the [[Maldives]], ''[[Culcita schmideliana]]'']] [[Image:Starfish closeup.jpg|thumb|200px|left|Closeup of the top surface of a starfish]] [[Image:red-knobbed.starfish.arp.jpg|right|thumb|200px|Red-knobbed starfish ''Protoreaster linckii'', a starfish from the Indian Ocean]] Starfish are composed of a central disc from which arms sprout in pentaradial symmetry. Most starfish have 5 arms, but some have more or fewer. Some starfish have shown differing numbers of limbs within a single species. The mouth is located underneath the starfish, on its ventral surface. The spiny upper surface is called the [[aboral]] or dorsal surface. On the aboral surface there is a structure called the [[madreporite]], a small white spot located slightly off-center on the central disc which acts as a water filter and supplies the starfish's water vascular system with water to move. Porcellanasteridae employ additional [[cribriform organs]] used to generate current in the burrows made by these infaunal starfish. While having their own basic body plan, starfish radiate diversely in shapes and colors, the morphology differing between each species. A starfish may have dense rows of spines as a means of protection, or it may have no spines at all. Ranging from nearly pentagonal (example: Indo-pacific cushion star, ''[[Culcita novaeguineae]]'') to gracile stars like those of the ''Zoroaster'' genus. [[Image:Henricia-sanguinolenta.jpg|thumb|200px|right|Blood star (''[[Henricia sanguinolenta]]'') at the [[New England Aquarium]], displaying its tube feet.]] Surrounding the spines on the surface of the starfish are small white objects known as [[pedicellariae]]. There are large numbers of these pedicellariae on the external body which serve to prevent encrusting organisms from colonizing the starfish. The radial canal which is across each arm of the starfish has tooth-like structures called [[ampullae]], which surround the radial canal. <!--The aboral surface is aell.--> On the end of each arm or ray there is a microscopic eye which allows the starfish to see, although it only allows it to see light and dark, which is useful to see movement. Patterns including mosaic-like tiles formed by ossicles, stripes, interconnecting net between spines, pustules with bright colors, mottles or spots. These mainly serve as camouflage or [[warning coloration]] which is displayed by many marine animals as a means of protection against predation. Several types of [[toxins]] and [[secondary metabolite]]s have been extracted from several species of starfish. Research into the efficacy of these compounds for possible pharmacological or industrial use occurs worldwide. ==Internal anatomy== [[Image:Asterias.svg|left|200px|thumb|Dissection of ''Asterias rubens''.]] The body cavity also contains the water vascular system that operates the [[tube feet]], and the [[circulatory system]], also called the '''hemal system'''. Hemal channels form rings around the mouth (the oral hemal ring), closer to the top of the starfish and around the digestive system (the gastric hemal ring). A portion of the body cavity called the axial sinus connects the three rings. Each ray also has hemal channels running next to the gonads. ===Digestion and excretion=== Starfish [[digestion]] is carried out in two [[stomach]]s: the cardiac stomach and the pyloric stomach. The cardiac stomach is a sack like stomach located at the center of the body and may be ''everted'' out of the organism's body to engulf and digest food. Some species are able to use their water vascular systems to force open the shells of [[bivalve]] [[mollusk]]s such as [[clam]]s and [[mussel]]s by injecting their stomachs into the shells. With the stomach inserted inside the shell, the starfish is able to digest the mollusk in place. The cardiac stomach is then brought back inside the body, and the partially digested food is moved to the pyloric stomach. Further digestion occurs in the intestine. Waste is either excreted through the anus on the [[aboral]] side of the body, or excreted through the mouth if the anus is absent as in [[brittle star]]s. Because of this ability to digest food outside of its body, the sea star is able to hunt prey that are much larger than its mouth would otherwise allow, including [[arthropod]]s, small [[fish]], and mollusks. Some echinoderms live several weeks without food under artificial conditions. It is believed that they may receive some nutrients from organic material dissolved in seawater. Sea stars and other echinoderms have [[endoskeleton]]s, suggesting that echinoderms are very closely related to [[chordate]]s; animals with a hollow nerve chord that usually have vertebrae. ==Variety== As mentioned above there are over 1800 species and many are undiscovered. Some of the better known starfish include: *[[Blue sea star]] *[[Japanese sea star]] *[[Carpet sea star]] *[[Eleven-armed sea star]] *[[Pincushion sea star]] *[[Comb sea star]] *[[Crown of thorns sea star]] *[[Common starfish]] A [[Japan|Japanese]] variety known locally as ''Gohongaze'' is considered an edible delicacy<ref name='cooking'> {{cite web|url=http://www.amakusa.tv/enewshito.html |title=Cooking Starfish In Japan |accessdate=2008-05-07 }}</ref>. ==Physiology== ===Nervous system=== Echinoderms have rather complex [[nervous system]]s, but lack a true centralized [[brain]]. All echinoderms have a network of interlacing nerves called a nerve plexus which lies within as well as below the skin. The [[esophagus]] is also surrounded by a number of nerve rings which send radial nerves that are often parallel with the branches of the water vascular system. The ring nerves and radial nerves coordinate the starfish's balance and directional systems. Although the echinoderms do not have many well-defined sensory inputs, they are sensitive to touch, light, temperature, orientation, and the status of water around them. The tube feet, spines, and pedicellariae found on starfish are sensitive to touch, while eyespots on the ends of the rays are light-sensitive. ===Diet=== [[Image:Starfishmussel.jpg|thumb|right|Sea star ''[[Pisaster ochraceus]]'' consuming a mussel in Central [[California]]]] Most species are generalist [[predators]], some eating [[clams]], and [[oysters]]; or any animal too slow to evade the attack (e.g. dying [[fish]]). Some species are detritivores, eating decomposed animal and plant material or organic films attached to substrate. The others may consume [[coral]] polyps (the best-known example for this is the infamous ''[[Acanthaster planci]]''), [[sea sponge|sponges]] or even suspended particles and [[plankton]]s (starfish from the Order [[Brisingida]]). The processes of feeding and capture may be aided by special parts; ''[[Pisaster brevispinus]]'' or Short-spined Pisaster from the [[Pacific Ocean|West Coast]] of America may use a set of specialized [[tube feet]] to extend itself deep into the soft substrata to extract prey (usually [[clam]]s)<ref>Nybakken ''Marine Biology: An Ecological Approach'', Fourth Edition, page 174. Addison-Wesley Educational Publishers Inc., 1997.</ref>. Grasping the shellfish, the Starfish slowly pries open the shell by wearing out the [[Adductor]] muscle and then inserts its stomach into an opening to devour the organism. ===Reproduction=== Starfish are capable of both sexual and asexual reproduction. Individual starfish are male or female. Fertilization takes place externally, both male and female releasing their [[gametes]] into the environment. Resulting fertilized embryos form part of the [[zooplankton]]. Starfish are developmentally ([[embryo]]logically) known as [[deuterostome]]s. Their embryo initially develops bilateral symmetry, indicating that starfish probably share a common ancestor with the [[chordates]], which includes the [[fish]]. Later development takes a very different path however as the developing starfish settles out of the zooplankton and develops the characteristic radial symmetry. Some species reproduce cooperatively, using environmental signals to coordinate the timing of gamete release; in other species, one to one pairing is the norm. Starfish commonly reproduce by free-spawning: releasing their gametes into the water where they hopefully are fertilized by gametes from the opposite sex. To increase their chances of fertilization, starfish probably gather in groups when they are ready to spawn, use environmental signals to coordinate timing (day length to indicate the correct time of the year, dawn or dusk to indicate the correct time of day), and may use chemical signals to indicate their readiness to each other. Fertilized eggs grow into [[bipinnaria]] and later into [[brachiolaria]] larvae, which either grow using a yolk or by catching and eating other plankton. In either case, they live as plankton, suspended in the water and swimming by using beating cilia. The larvae are bilaterally symmetric — unlike adults, they have a distinct left and right side. Eventually, they undergo a complete metamorphosis, settle to the bottom, and grow into adults.Some species of starfish brood their young: the males spawn gametes which fertilize eggs held by the females. The females may hold the eggs on their surface, in the pyloric stomach (as in ''Leptasterias tenera''), or even attach them to the ground (as in ''Asterina gibbosa''). Brooding is especially common in polar and deep-sea species, environments less favourable for larvae. Male and female starfish are not distinguishable from the outside; one needs to see the gonads or be lucky enough to catch them spawning. The gonads are located in each arm, and release gametes through gonoducts located on the central body between the arms. Some species of starfish also reproduce asexually by fragmentation, often with part of an arm becoming detached and eventually developing into an independent individual starfish. This has led to some notoriety. Starfish can be pests to fishermen who make their living on the capture of clams and other mollusks at sea as starfish prey on these. The fishermen would presumably kill the starfish by chopping them up and disposing of them at sea, ultimately leading to their increased numbers until the issue was better understood. A starfish arm can only regenerate into a whole new organism if some of the central ring of the starfish is part of the chopped off arm. ===Locomotion=== [[Image:Stachelhaeuter fg01.jpg|thumb|left|The underside of a sea star. The inset shows a magnified view of the tube feet.]] Sea stars move using a water vascular system. Water comes into the system via the madreporite. It is then circulated from the stone canal to the ring canal and into the radial canals. The radial canals carry water to the ampullae and provide suction to the tube feet. The tube feet latch on to surfaces and move in a wave, with one body section attaching to the surfaces as another releases. Most starfish cannot move quickly. However, some burrowing species like starfish from genus ''[[Astropecten]]'' and ''[[Luidia]]'' are capable of rapid, creeping motion: "gliding" across the ocean floor. This motion results from their pointed tubefeet adapted specially for excavating patches of sand. [[Image:Starfish Roentgen X-Ray 01 Nevit.jpg|thumb|Starfish skeleton]] ===Regeneration=== [[Image:Sea star regenerating legs.jpg|thumb|left|A sunflower starfish is regenerating arms that were lost to predators]] Some species of starfish have the ability to regenerate lost arms and can regrow an entire new arm in time. Most species must have the central part of the body intact to be able to regenerate, but a few can grow an entire starfish from a single ray. Included in this group are the red and blue ''Linckia'' star. The regeneration of these stars is possible due to the vital organs kept in their arms. ==Geological history== The larvae of echinoderms are ciliated, free-swimming organisms. They tend to look like embryonic chordates because they organize themselves bilaterally. As the organism grows, one side of the body grows more than the other, and eventually absorbs the smaller side. After that, the body is formed into five parts around a central axis. Then the echinoderm has radial symmetry. ==Distribution== There are about 1,800 known living species of starfish, and they occur in all of the Earth's oceans. The greatest variety of starfish is found in the tropical Indo-Pacific. Areas known for their great diversity include the tropical-temperate regions around Australia, the tropical East Pacific, and the cold-temperate water of the North Pacific (California to Alaska). ''[[Asterias]]'' is a common genus found in [[Europe]]an waters and on the eastern coast of the [[United States]]; ''[[Pisaster]]'', along with ''Dermasterias'' ("leather star"), are usually found on the western coast. Habitats range from [[tropical]] [[coral reefs]], [[kelp forest]]s to deep-sea floor, although none of them live within the water column; all species of starfish found are living as [[benthos]]. [[Echinoderms]] need a delicate internal balance in their body; no starfish are found in [[freshwater]] environments. ==Notes== {{reflist}} == References == * Blake DB, Guensburg TE; Implications of a new early Ordovician asteroid (Echinodermata) for the phylogeny of Asterozoans; Journal of Paleontology, 79 (2): 395-399; MAR 2005. * Gilbertson, Lance; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999). * Shackleton, Juliette D.; Skeletal homologies, phylogeny and classification of the earliest asterozoan echinoderms; Journal of Systematic Palaeontology; 3 (1): 29-114; March 2005. * Solomon, E.P., Berg, L.R., Martin, D.W. 2002. Biology, Sixth Edition. * Sutton MD, Briggs DEG, Siveter DJ, Siveter DJ, Gladwell DJ; A starfish with three-dimensionally preserved soft parts from the Silurian of England; Proceedings of the Royal Society B - Biological Sciences; 272 (1567): 1001-1006; MAY 22 2005. *Hickman C.P, Roberts L.S, Larson A., l'Anson H., Eisenhour D.J.; Integrated Principles of Zoology; McGraw Hill; New York; ISBN 0-07-111593-5 (Thirteenth edition; 2006). ===Resources=== {{wikispecies|Asteroidea}} {{commonscat|Asteroidea}} *[http://www.vma.cape.com/~jdale/science/science.htm Starfish Science] *[http://www.tolweb.org/Asteroidea/19238 From the Tree of Life project] *[http://www.calacademy.org/research/izg/echinoderm/classify.htm Classification of the Extant Echinodermata] *[http://users.bigpond.net.au/je.st/starfish/index.html Starfish Home Page] *[http://www.b-visible.co.uk/article/starfish.html Starfish Population Explosion] *[http://www.starfish.ch/collection/seesterne.html Photos of Sea Stars] ==Gallery== <gallery> Image:Sun flower sea star in tide pools.jpg|Sun flower sea star in [[ tide pool]] in [[California]]. Image:White Sea StarFish, Russia.jpg|[[White Sea]] starfish, [[Russia]]. Image:Sculpin is eating Leptasterias hexactis.jpg|[[Tide pool]] [[sculpin]] is eating ''Leptasterias hexactis''. Image:Blue starfish.JPG|Blue starfish in [[Papua New Guinea]]. Image:Star Fish at Montana de Oro.JPG|Bat star, ''[[Asterina miniata]]''. Image:Ochre sea star on beach, Olympic National Park USA.jpg|[[Ochre sea star]], ''Pisaster ochraceus'' on beach at [[Olympic National Park]], USA. Image:Orange ochre star.jpg|An ochre star in [[Bamfield]], [[Canada]] Image:Granulated sea star.jpg|Granulated sea star on [[Meedhupparu]] house reef in the [[Maldives]], ''[[Choriaster granulatus]]''. Image:Guildings's sea star.jpg|Guilding's sea star on [[Meedhupparu]] house reef in the [[Maldives]], ''[[Linkia guildingi]]''. Image:Sandstar 300.jpg|''Pisaster giganteus,'' the [[Giant sea star]]. Image:starfish.jpg|The tube feet can be seen on this starfish. </gallery> [[Category:Asteroidea| ]] [[Category:Echinoderms]] [[ar:نجم البحر]] [[bs:Morske zvijezde]] [[ca:Estrella de mar]] [[da:Søstjerne]] [[de:Seesterne]] [[et:Meritähed]] [[es:Asteroidea]] [[eo:Marstelo]] [[fa:ستاره دریایی]] [[fr:Étoile de mer]] [[ko:불가사리류]] [[io:Asterio]] [[id:Bintang laut]] [[is:Krossfiskar]] [[it:Asteroidea]] [[he:כוכבי ים]] [[ka:ზღვის ვარსკვლავები]] [[ht:Etwaldemè]] [[lt:Jūrų žvaigždės]] [[hu:Tengericsillagok]] [[ml:നക്ഷത്രമത്സ്യം]] [[nl:Zeesterren]] [[ja:ヒトデ]] [[no:Sjøstjerner]] [[oc:Estela de mar]] [[pl:Rozgwiazdy]] [[pt:Estrela-do-mar]] [[qu:Yaku quyllur]] [[ru:Морские звёзды]] [[simple:Sea star]] [[sk:Hviezdovky]] [[sl:Morske zvezde]] [[sr:Морске звезде]] [[fi:Meritähdet]] [[sv:Sjöstjärnor]] [[tl:Isdambituin]] [[th:ดาวทะเล]] [[tr:Denizyıldızı]] [[uk:Морські зірки]] [[vls:Zêesterre]] [[zh:海星]]