Examine individual changes

'{{For|the punk rock band|Hagfish (band)}} {{distinguish|Hogfish}} {{Taxobox | name=Hagfish | image=Pacific_hagfish_Myxine.jpg | image_caption=[[Pacific hagfish]] resting on the ocean bottom, at 280&nbsp;m depth off the [[Oregon]] coast | regnum=[[Animal]]ia | phylum=[[Chordate|Chordata]] | subphylum=[[Vertebrata]] | superclassis=[[Cyclostomata]] | classis='''Myxini''' | ordo='''Myxiniformes''' | familia='''Myxinidae''' | familia_authority=[[Constantine Samuel Rafinesque|Rafinesque]], 1815 | subdivision_ranks=[[Genus|Genera]]<ref name="Nelson">{{cite book|last1=Nelson|first1=Joseph S.|last2=Grande|first2=Terry C.|last3=Wilson|first3=Mark V. H.|year=2016|title=''Fishes of the World''|edition=5th|publisher=[[John Wiley & Sons]]|isbn=9781118342336}}</ref> | subdivision = * [[Rubicundinae]] <small>Fernholm et al. 2013</small> ** ''[[Rubicundus]]'' <small>Fernholm et al. 2013</small> * [[Eptatretinae]] <small>Bonaparte 1850</small> ** ''[[Eptatretus]]'' <small>Cloquet 1819</small> * [[Myxininae]] <small>Nelson 1976</small> ** ''[[Myxine]]'' <small>Linnaeus 1758</small> ** ''[[Nemamyxine]]'' <small>Richardson 1958</small> ** ''[[Neomyxine]]'' <small>Richardson 1953</small> ** ''[[Notomyxine]]'' <small>Nani & Gneri 1951</small> | synonyms= * Bdellostomatidae <small>Gill 1872</small> * Homeidae <small>Garman 1899</small> * Paramyxinidae <small>Berg 1940</small> * Diporobranchia <small>Latreille 1825</small><ref name="van der Laan et al.">{{cite journal|last1=van der Laan|first1=Richard|last2=Eschmeyer|first2=William N.|last3=Fricke |first3=Ronald|year=2014|title=''Family-group names of Recent fishes''|volume=3882|issue=2|journal=[[Zootaxa]]|publisher=Magnolia Press|pages=001–230|url=https://dx.doi.org/10.11646/zootaxa.3882.1.1|issn=1175-5326}}</ref> }} '''Hagfish''', the class [[Cyclostomata|'''Myxini''']] (also known as '''Hyperotreti'''), are [[eel]]-shaped, slime-producing marine [[fish]] (occasionally called '''slime eels'''). They are the only known living animals that have a [[skull]] but no [[vertebral column]], although hagfish do have rudimentary vertebrae.<ref name=":0">{{Cite book|title=Campbell Biology|last=Reece|first=Jane|publisher=Pearson|year=2014|isbn=0321775651|location=Boston|pages=717}}</ref> Along with [[lampreys]], hagfish are jawless; they are the sister group to jawed vertebrates, and living hagfish remain similar to hagfish from around 300 million years ago.<ref>[http://www.ucmp.berkeley.edu/vertebrates/basalfish/myxini.html Myxini] – University of California Museum of Paleontology</ref> The classification of hagfish had been controversial<!-- citation -->. The issue was whether the hagfish was a degenerate type of vertebrate-fish that through evolution had lost its vertebrae (the original scheme) and was most closely related to lampreys, or whether hagfish represent a stage that precedes the evolution of the vertebral column (the alternative scheme) as is the case with [[lancelets]]. Recent DNA evidence has supported the original scheme.<ref name=r3>{{cite journal|author=Janvier, P.|author-link=Philippe Janvier|year= 2010|title=MicroRNAs revive old views about jawless vertebrate divergence and evolution|journal= Proceedings of the National Academy of Sciences |volume=107|pages=19137–19138|quote=Although I was among the early supporters of vertebrate paraphyly, I am impressed by the evidence provided by Heimberg et al. and prepared to admit that cyclostomes are, in fact, monophyletic. The consequence is that they may tell us little, if anything, about the dawn of vertebrate evolution, except that the intuitions of 19th century zoologists were correct in assuming that these odd vertebrates (notably, hagfishes) are strongly degenerate and have lost many characters over time|doi=10.1073/pnas.1014583107|issue=45|bibcode= 2010PNAS..10719137J|pmid=21041649|pmc=2984170}}</ref> The original scheme groups hagfish and lampreys together as [[cyclostomata|cyclostomes]] (or historically, [[Agnatha]]), as the oldest surviving class of [[vertebrates]] alongside [[gnathostomes]] (the now-ubiquitous jawed vertebrates). The alternative scheme proposed that jawed vertebrates are more closely related to lampreys than to hagfish (i.e., that vertebrates include lampreys but exclude hagfish), and introduces the category [[craniata]] to group vertebrates near hagfish. ==Physical characteristics== [[File:NIE 1905 Hagfish - Myxine glutinosa.jpg|thumb|left|Two views of the hagfish (''Myxini glutinosa'') with analytical overlays and dissection, published 1905]] ===Body features=== Hagfish are typically about {{convert|0.5|m|in|1|abbr=on}} in length. The largest known species is ''[[Eptatretus goliath]]'', with a specimen recorded at {{convert|127|cm|ftin|abbr=on}}, while ''[[Myxine kuoi]]'' and ''[[Myxine pequenoi]]'' seem to reach no more than {{convert|18|cm|in|abbr=on}} (some have been seen as small as {{convert|4|cm|in|abbr=on}}). Hagfish have elongated, eel-like bodies, and [[paddle]]-like [[tail]]s. The skin is naked and covers the body like a loosely fitting sock. They have [[cartilage|cartilaginous]] [[skull]]s (although the part surrounding the brain is composed primarily of a fibrous sheath) and [[tooth]]-like structures composed of [[keratin]]. [[Color]]s depend on the [[species]], ranging from [[pink]] to [[blue]]-[[grey]], and [[black]] or [[white]] spots may be present. [[Eye]]s are simple eyespots, not compound eyes that can resolve images. Hagfish have no true [[fin]]s and have six or eight [[barbel (anatomy)|barbel]]s around the mouth and a single [[nostril]]. Instead of vertically articulating [[jaw]]s like [[Gnathostomata]] ([[vertebrate]]s with jaws), they have a pair of [[horizontal plane|horizontally]] moving structures with tooth-like projections for pulling off food. The mouth of the hagfish has two pairs of horny, comb-shaped teeth on a cartilaginous plate that protracts and retracts. These teeth are used to grasp food and draw it toward the pharynx.<ref name=r1>[http://tolweb.org/Hyperotreti Hyperotreti]. Tree of Life</ref> [[Image:Eptatretus stoutii.jpg|thumb|[[Pacific hagfish]] at 150 m depth, [[California]], [[Cordell Bank National Marine Sanctuary]]]] Its skin is only attached to the body along the center ridge of the back and at the slime glands, and is filled with close to a third of the body's blood volume, giving the impression of a blood-filled sack. It is assumed this is an adaptation to survive predator attacks.<ref>[https://www.popsci.com/shark-hagfish-flaccid-skin-sack The world's fastest shark is no match for a sack of flaccid hagfish skin]</ref> ===Slime=== [[File:Eptatretus stoutii 1.jpg|thumb|right|[[Pacific hagfish]] trying to hide under a rock]] Hagfish are long and [[wikt:vermiform|vermiform]], and can exude copious quantities of a milky and fibrous slime or [[mucus]] from some 100 glands or [[invaginations]] running along their flanks.<ref name=r2>{{cite news | last=Rothschild | first=Anna | title=Hagfish slime: The clothing of the future? | url= http://www.bbc.co.uk/news/magazine-21954779 | publisher=BBC News | date= 2013-04-01 | accessdate=2013-04-02}}</ref> The species ''Myxine glutinosa'' was named for this slime. When captured and held, e.g., by the tail, they secrete the microfibrous slime, which expands into up to 20 litres (5¼ US gallons) of sticky, gelatinous material when combined with water.<ref>{{cite web|title=Snotties at Southern Encounter |url=http://www.southernencounter.co.nz/seanews_whatsnew.htm |publisher=Southern Encounter Aquarium and Kiwi House |date=2007-10-30 |accessdate=2008-10-30 |deadurl=yes |archiveurl=https://web.archive.org/web/20130607101234/http://www.southernencounter.co.nz/seanews_whatsnew.htm |archivedate=June 7, 2013 }}</ref> If they remain captured, they can tie themselves in an [[overhand knot]], which works its way from the head to the tail of the animal, scraping off the slime as it goes and freeing them from their captor. This singular behavior may assist them in extricating themselves from the jaws of predatory fish or from the interior of their own "prey", and the "sliming" might act as a distraction to predators. Recently, the slime was reported to entrain water in its microfilaments, creating a slow-to-dissipate, viscoelastic substance, rather than a simple gel. It has been proven to impair the function of a predator fish's [[gill]]s. In this case, the hagfish's mucus would clog the predator's gills, disabling their ability to breathe. The predator would release the hagfish to avoid suffocation. Because of the mucus there are few marine predators that target the hagfish. Other predators of hagfish are varieties of birds or mammals.<ref>{{cite journal |doi=10.1242/jeb.02067 |last1=Lim |first1=J |last2=Fudge |first2=DS |last3=Levy |first3=N |last4=Gosline |first4=JM |title=Hagfish slime ecomechanics: testing the gill-clogging hypothesis |date=January 31, 2006 |journal=Journal of Experimental Biology |volume=209|issue=Pt 4 | pages=702–710 |pmid=16449564 }}</ref> Free-swimming hagfish also "slime" when agitated, and later clear the mucus utilizing the same travelling-knot behavior.<ref>{{Cite book |last=Martini |first=F. H. |year=1998 |chapter=The ecology of hagfishes |title=The Biology of Hagfishes |editor-first=J. M. |editor-last=Jørgensen |editor2-first=J. P. |editor2-last=Lomholt |editor3-first=R. E. |editor3-last=Weber |editor4-first=H. |editor4-last=Malte |pages=57–77 |place=London |publisher=Chapman and Hall |isbn=0-412-78530-7 |chapterurl=https://books.google.com/books?id=vu1uzL0p7xsC&pg=PA57 }}</ref><ref>{{Cite journal |author=Strahan, R. |year=1963 |title=The behavior of myxinoids |journal=Acta Zool. |volume=44 |pages=73–102 |doi=10.1111/j.1463-6395.1963.tb00402.x}}</ref> The reported gill-clogging effect suggests that the travelling-knot behavior is useful or even necessary to restore the hagfish's own gill function after "sliming". Hagfish slime is under investigation as an alternative to spider silk for use in applications such as body armor.<ref>{{Cite news|url=https://nypost.com/2017/10/25/slime-from-this-300-million-year-old-creature-could-create-bulletproof-body-armor/|title=Slime from this 300 million-year-old creature could create bulletproof body armor|date=2017-10-25|work=New York Post|access-date=2017-10-26|language=en-US}}</ref> ===Respiration=== Hagfish generally respire by taking in water through their [[pharynx]], past the velar chamber and bringing the water through the internal [[gill]] pouches, which can vary in number from 5 to 16 pairs, depending on species.<ref>{{cite book|author1=Springer, Joseph |author2=Holley, Dennis |title=An Introduction to Zoology|url=https://books.google.com/books?id=BzgNZca_L5AC&pg=PA376|date=2012|publisher=Jones & Bartlett Publishers|isbn=978-1-4496-9544-6|pages=376–}}</ref> The gill pouches open individually, but in Myxine the openings have coalesced, with canals running backwards from each opening under the skin, uniting to form a common aperture on the [[ventral]] side known as the branchial opening. The [[esophagus]] is also connected to the left branchial opening, which is therefore larger than the right one, through a pharyngocutaneous duct (esophageocutaneous duct), which has no respiratory tissue. This pharyngocutaneous duct is used to clear large particles from the pharynx, a function also partly taking place through the nasopharyngeal canal. In other species the coalescence of the gill openings is less complete, and in Bdellostoma each pouch opens separately to the outside like in lampreys.<ref>{{cite book|author=Hughes, George Morgan |title=Comparative Physiology of Vertebrate Respiration|url=https://books.google.com/books?id=yy99QtoPEToC&pg=PA9|date=1963|publisher=Harvard University Press|isbn=978-0-674-15250-2|pages=9–}}</ref><ref>{{cite book|author=Wake, Marvalee H. |title=Hyman's Comparative Vertebrate Anatomy|url=https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA81|date=1992|publisher=University of Chicago Press|isbn=978-0-226-87013-7|pages=81–}}</ref> The unidirectional water flow passing the gills is produced by rolling and unrolling velar folds located inside a chamber developed from the naso-hypophyseal tract, and is operated by a complex set of muscles inserting into cartilages of the neurocranium, assisted by peristaltic contractions of the gill pouches and their ducts.<ref>{{cite book|author1=Bone, Quentin |author2=Moore, Richard |title=Biology of Fishes|url=https://books.google.com/books?id=e2N4AgAAQBAJ&pg=PA128|date= 2008|publisher=Taylor & Francis|isbn=978-1-134-18631-0|pages=128–}}</ref> Hagfish also have a well-developed dermal capillary network that supplies the skin with oxygen when the animal is buried in anoxic mud, as well as a high tolerance for both hypoxia and anoxia, with a well developed anaerobic metabolism.<ref name ="Jørgensen" >{{cite book|author=Jørgensen, Jørgen Mørup |title=The Biology of Hagfishes|url=https://books.google.com/books?id=vu1uzL0p7xsC&pg=PA231|year=1998|publisher=Springer Science & Business Media|isbn=978-0-412-78530-6|pages=231–}}</ref> It has also been suggested that the skin is capable of [[cutaneous respiration]].<ref>{{cite book|author1=Helfman, Gene |author2=Collette, Bruce B. |author3=Facey, Douglas E. |author4=Bowen, Brian W. |title=The Diversity of Fishes: Biology, Evolution, and Ecology|url=https://books.google.com/books?id=FyehAR6hsUUC&pg=PA235|date= 2009|publisher=John Wiley & Sons|isbn=978-1-4443-1190-7|pages=235–}}</ref> ===Nervous System=== ===Eye=== The hagfish's eye, which lacks a lens, [[extraocular muscles]], and the three motor cranial nerves (III, IV, and VI), is significant to the [[Evolution of the eye|evolution of more complex eyes]]. A [[parietal eye]] and the [[parapineal organ]] are also absent in extant hagfish.<ref>{{cite book|author=Ostrander, Gary Kent |title=The Laboratory Fish|url=https://books.google.com/books?id=Hp4YSFiSD0IC&pg=PT129|year=2000|publisher=Elsevier|isbn=978-0-12-529650-2|pages=129–}}</ref><ref>{{cite web|url=http://www.physorg.com/news115919015.html|title=Keeping an eye on evolution|date=2007-12-03|accessdate=2007-12-04|publisher=PhysOrg.com}}</ref> Hagfish eyespots, when present, can detect light, but as far as it is known, none can resolve detailed images. In ''Myxine'' and ''Neomyxine'', the eyes are partly covered by the trunk musculature.<ref name=r1/> Paleontological evidence suggests, however, that the hagfish eye is not [[Cladistics|pleisiomorphic]] but rather degenerative, as fossils from the Carboniferous have revealed hagfish-like vertebrates with complex eyes. This would suggest that ancestrally Myxini possesed complex eyes. <ref> {{Citation| last1 = Gabbott | first1 = S.E, | last2 = Donoghu | first2 = P.C, | last3 = Sansom | first3 = R.S, | last4 = Vinther | first4 = J | display-authors = 2 | title = Pigmented anatomy in Carboniferous cyclostomes and the evolution of the vertebrate eye. | journal = Proc. R. Soc. B | volume = 283 | issue = 1836 | year = 2016 }} </ref> <ref> {{Citation| last1 = Bardack | first1 = D, | title = First fossil hagfish (Myxinoidea): a record from the Pennsylvanian of Illinois | journal = Science | volume = 254 | issue = 5032 | year = 1991 }} </ref> ===Cardiac function, circulation and fluid balance=== Hagfish is known to have one of the lowest blood pressures among the vertebrates.<ref>{{Cite journal|last=Forster|first=Malcolm E.|last2=Axelsson|first2=Michael|last3=Farrell|first3=Anthony P.|last4=Nilsson|first4=Stefan|date=1991-07-01|title=Cardiac function and circulation in hagfishes|url=http://www.nrcresearchpress.com/doi/10.1139/z91-277|journal=Canadian Journal of Zoology|volume=69|issue=7|pages=1985–1992|doi=10.1139/z91-277|issn=0008-4301}}</ref>One of the most primitive type of fluid balance found is among these creatures, whenever there is a rise in extracellular fluid, the blood pressure rises and this in turn is sensed by the kidney which excretes excess fluid.<ref name ="Jørgensen"/> They also have the highest blood volume to body mass of any chordate, with 17 ml of blood per 100 g of mass. <ref>[http://cronodon.com/BioTech/hagfish.html Hagfish - Cronodon]</ref> The hagfish circulatory system has been of considerable interests to evolutionary biologists, who first believed that the hagfish heart was not innervated like that in jawed vertebrates. <ref> {{Citation| last1 = Jensen | first1 = D, | title = The aneural heart of the hagfish. | journal = Annals of the New York Academy of Sciences | volume = 127 | issue = 1 | year = 1965 }} </ref> Further investigation revealed that the hagfish did have a true innervated heart. The hagfish circulatory system also consists of multiple accessory pumps throughout the body which are considered auxiliary “hearts”. <ref>{{Cite journal|last=Forster|first=Malcolm E.|last2=Axelsson|first2=Michael|last3=Farrell|first3=Anthony P.|last4=Nilsson|first4=Stefan|date=1991-07-01|title=Cardiac function and circulation in hagfishes|url=http://www.nrcresearchpress.com/doi/10.1139/z91-277|journal=Canadian Journal of Zoology|volume=69|issue=7|pages=1985–1992|doi=10.1139/z91-277|issn=0008-4301}}</ref> Hagfish are the only known vertebrates with osmoregulation isosmotic to their external environment. Hypothetically, they excrete ions in bile salts. <ref> {{Citation| last1 = Robertson | first1 = J.D, | title = Chemical composition of the body fluids and muscle of the hagfish Myxine glutinosa and the rabbit‐fish Chimaera monstros. | journal = Journal of Zoology | volume = 178 | issue = 2 | year = 1976 }} </ref> ===Musculo-Skeletal System=== Hagfish musculature differs from jawed vertebrates in that they do not have a [[horizontal septum]] nor [[vertical septum]], junctions of connective tissue that separate the [[hypaxial musculature]] and [[epaxial musculature]]. They do, however, have true myomeres and myosepta like all vertebrates. The mechanics of their craniofacial muscles in feeding have been investigated, revealing advantages and disadvantages of the dental plate. In particular, hagfish muslces have increased force and gape size compared to similar-sized jawed vertebrates but lack the speed amplification, suggesting that jaws are faster acting.. <ref> {{Citation| last1 = Clark | first1 = A.J, | last2 = Summers | first2 = A.P | display-authors = 2 | title = Morphology and kinematics of feeding in hagfish: possible functional advantages of jaws. | journal = Journal of Experimental Biology | volume = 210 | issue = 22 | year = 2007 | pages = 3897-3909 }} </ref> [[File:Hagfish trunk.jpg|thumb|left|Horizontal section of hagfish midline trunk. The notochord is the only skeletal element and the musculature lacks a horizontal and vertical septum.]] The hagfish skeleton comprises the skull, the notochord, and the caudal fin rays. <ref> {{Citation| last1 = Cole | first1 = F.J, | title = A Monograph on the general Morphology of the Myxinoid Fishes, based on a study of Myxine. Part I. The Anatomy of the Skeleton. | journal = Earth and Environmental Science Transactions of The Royal Society of Edinburgh | volume = 41 | issue = 3 | year = 1906 }} </ref> In Cole's monograph (1906)<!-- citation -->, he described sections of the skeleton that he termed "pseudo-cartilage," referring to its distinct properties compared to jawed chordates. The lingual apparatus of hagfish is composed of a cartilage base bearing two teeth-covered plates (dental plate) articulated with a series of large cartilage shafts<!-- citation -->. The nasal capsule is considerably expanded in hagfish, comprising a fibrous sheath lined with cartilage rings. In contrast to lamprey, the braincase is non-cartilaginous. The role of the branchial arches is highly speculative, as hagfish embryos undergo a caudal shift of the posterior pharyngeal pouches, and thus, the branchial arches do not support gills. <ref> {{Citation| last1 = Oisi | first1 = Y, | last2 = Fujimoto | first2 = S | last3 = Ota | first3 = K.G | last4 = Kuratani | first4 = S | display-authors = 4 | title = On the peculiar morphology and development of the hypoglossal, glossopharyngeal and vagus nerves and hypobranchial muscles in the hagfish. | journal = Zoological letters | volume = 1 | issue = 1 | year = 2015 }} </ref> ==Reproduction== [[Image:Eptatretus polytrema.jpg|thumb|right|Drawing of ''[[Eptatretus polytrema]]'']] [[Image:Eptatretus cirrhatus (New Zealand hagfish).gif|thumb|right|Drawing of a [[New Zealand hagfish]]]] Very little is known about hagfish reproduction. Embryos are difficult to obtain for study, although laboratory breeding of the Far Eastern [[inshore hagfish]], ''[[Eptatretus burgeri]]'', has succeeded.<ref>{{cite journal|pmid=17691082|year=2007|last1=Holland|first1=ND|title=Hagfish embryos again: The end of a long drought|volume=29|issue=9|pages=833–6|doi=10.1002/bies.20620|journal=BioEssays}}</ref> In some species, sex ratio has been reported to be as high as 100:1 in favor of females. Some hagfish species are thought to be [[hermaphroditic]], having both an [[ovary]] and a [[testicle]] (there is only one gamete production organ in both females and males). In some cases, the ovary is thought to remain nonfunctional until the individual has reached a particular age or encounters a particular environmental stress. These two factors in combination suggest the survival rate of hagfish is quite high. Depending on species, females lay from one to thirty tough, yolky eggs. These tend to aggregate due to having [[Hook and loop fastener|Velcro]]-like tufts at either end. Hagfish are sometimes seen curled around small clutches of eggs. It is not certain if this constitutes actual breeding behavior. Hagfish do not have a [[larva]]l stage, in contrast to [[lamprey]]s, which have a long one. Hagfish have a [[mesonephros|mesonephric kidney]] and are often [[Neoteny|neotenic]] of their [[pronephros|pronephric kidney]]. The kidney(s) are drained via mesonephric/[[archinephric duct]]. Unlike many other vertebrates, this duct is separate from the reproductive tract. Unlike all other vertebrates, the proximal tubule of the [[nephron]] is also connected with the [[coelom]], provided lubrication.{{Citation needed|date=April 2011}} The single testicle or ovary has no transportation duct. Instead, the gametes are released into the coelom until they find their way to the posterior end of the [[Caudal (anatomical term)|caudal]] region, whereby they find an opening in the digestive system. Development of the hagfish embryo is retarded in comparison to other jawless vertebrates, taking as long as eleven months before hatching. <ref>{{cite journal| year=1997|last1=Gorbman|first1=A|title=Hagfish development|journal = Zoological science | volume = 14|issue=3| pages=375–390 }}</ref> Thus, information on their embryology has been obscured until recently when husbandry advances have enabled considerable advances to the understanding of the group's evolutionary development. Their development has provided new insights into the evolution of [[neural crest cells]], solidifying the consensus that these cells are a shared trait by all vertebrates and that these cells are regulated by a common subset of genes. <ref>{{cite journal| year=2007 |last1=Ota|first1=K.G| last2=Kuraku | first2 = S. | last3 = Kuratani | first3 = S | display-authors = 1 | title = Hagfish embryology with reference to the evolution of the neural crest|journal =Nature | volume = 446|issue=7136}}</ref> ==Feeding== [[Image:Pacific hagfish feeding 01.jpg|thumb|left|Two Pacific hagfish feeding on a dead sharpchin rockfish, ''[[Sebastes zacentrus]]'', while one remains in a curled position at the left of the photo]] While [[polychaete]] [[marine worm]]s on or near the sea floor are a major food source, hagfish can feed upon and often even enter and eviscerate the bodies of dead and dying/injured sea creatures much larger than themselves. They are known to devour their prey from the inside.<ref>Wilson, Hugh (November 2009) [https://web.archive.org/web/20091116002431/http://green.ca.msn.com/green-living/gallery.aspx?cp-documentid=22580760&page=6 Hagfish – World's weirdest animals]. green.ca.msn.com</ref> Hagfish have the ability to absorb dissolved organic matter across the skin and gill, which may be an adaptation to a scavenging lifestyle, allowing them to maximize sporadic opportunities for feeding. From an evolutionary perspective, hagfish represent a transitory state between the generalized nutrient absorption pathways of aquatic invertebrates and the more specialized digestive systems of aquatic vertebrates.<ref>{{cite journal|last=Glover|first=CN|author2=Bucking, C |author3=Wood, CM |title=Adaptations to in situ feeding: novel nutrient acquisition pathways in an ancient vertebrate|journal=Proceedings of the Royal Society B: Biological Sciences |date=2011-03-02|pmid=21367787|doi=10.1098/rspb.2010.2784|volume=278|issue=1721|pages=3096–101|pmc=3158932}}</ref> Like [[leech]]es, they have a sluggish metabolism and can survive months between feedings;<ref>{{cite web|title=Introduction to the Myxini|url=http://www.ucmp.berkeley.edu/vertebrates/basalfish/myxini.html|accessdate=2009-01-25|work=Berkeley.edu website}}</ref><ref>{{cite journal|doi=10.1016/S0022-0981(96)02665-2|last1=Lesser|first1=M|title=Ecology of the hagfish, Myxine glutinosa L. in the Gulf of Maine I. Metabolic rates and energetics |journal=Journal of Experimental Marine Biology and Ecology | volume=208 | date=3 January 1997|issue=1–2 | pages=215–225|last2=Martini|first2=Frederic H.|last3=Heiser|first3=John B. }}</ref> their feeding behavior, however, appears quite vigorous. Analysis of the stomach content of several species has revealed a large variety of prey, including [[polychaetes]], shrimps, [[hermit crab]]s, [[cephalopods]], [[brittlestar]]s, [[bony fish]]es, sharks, birds and whale flesh.<ref>{{Cite journal | doi = 10.3354/meps10341|url=http://www.int-res.com/articles/meps_oa/m485p223.pdf | title = Hagfish feeding habits along a depth gradient inferred from stable isotopes| journal = Marine Ecology Progress Series| volume = 485| pages = 223–234| year = 2013| last1 = Zintzen | first1 = V. | last2 = Rogers | first2 = K. M. | last3 = Roberts | first3 = C. D. | last4 = Stewart | first4 = A. L. | last5 = Anderson | first5 = M. J. }}</ref> In captivity, hagfish are observed to use the overhand-knot behavior "in reverse" (tail-to-head) to assist them in gaining mechanical advantage to pull out chunks of flesh from carrion fish or cetaceans, eventually making an opening to permit entry to the interior of the body cavity of larger carcasses. A healthy larger sea creature likely would be able to outfight or outswim this sort of assault. This energetic opportunism on the part of the hagfish can be a great nuisance to fishermen, as they can devour or spoil entire deep-drag-netted catches before they can be pulled to the surface. Since hagfish are typically found in large clusters on and near the bottom, a single trawler's catch could contain several dozen or even hundreds of hagfish as bycatch, and all the other struggling, captive sea life make easy prey for them. The digestive tract of the hagfish is unique among the chordates because the food in the gut is enclosed in a permeable membrane, analogous to the [[peritrophic matrix]] of insects.<ref>[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press (publisher)|Greenwood Press]].</ref> Hagfish have also been observed actively [[predation|hunting]] the red bandfish, ''[[Cepola haastii]]'', in its burrow, possibly using their slime to suffocate the fish before grasping it with their dental plates and dragging it from the burrow.<ref>{{Cite journal | last1 = Zintzen | first1 = V. | last2 = Roberts | first2 = C. D. | last3 = Anderson | first3 = M. J. | last4 = Stewart | first4 = A. L. | last5 = Struthers | first5 = C. D. | last6 = Harvey | first6 = E. S. | title = Hagfish predatory behaviour and slime defence mechanism | doi = 10.1038/srep00131 | journal = Scientific Reports | volume = 1 | year = 2011 | pmid = 22355648| pmc = 3216612}}</ref> ==Classification== Originally, ''Myxine'' was included by Linnaeus (1758) in [[Vermes]]. A single fossil of hagfish shows little evolutionary change has occurred in the last 300 million years.<ref>{{cite web|url=http://www.networksplus.net/maxmush/myxinidae.html |title=Myxinidae Information |publisher=Mudminnow Information Services |accessdate=2010-08-05 |deadurl=yes |archiveurl=https://web.archive.org/web/20080702222154/http://www.networksplus.net/maxmush/myxinidae.html |archivedate=July 2, 2008 }}</ref> In recent years, hagfish have become of special interest for genetic analysis investigating the relationships among [[chordate]]s. Their classification as [[agnatha]]ns places hagfish as elementary [[vertebrate]]s in between [[invertebrate]]s and [[gnathostome]]s. However, there has been long discussion in scientific literature about whether the hagfish were even [[Invertebrate|non-vertebrate]]. Using fossil data, paleontologists posited that lamprey are closer related to gnathostomes than hagfish. The term “Craniata” was used to refer to animals that had a developed skull but were not considered true vertebrates. <ref>{{cite journal| year=1993 |last1=Forey|first1=P| last2=Janvier | first2 = P. | display-authors = 2 | title = Agnathans and the origin of jawed vertebrates|journal =Nature | volume = 361|issue=6408 }}</ref> Molecular evidence in the early 1990’s first began suggesting that lampreys and hagfish were closer related to each other than to gnathostomes. <ref>{{cite journal| year=1992 |last1=Stock|first1=D.W| last2=Whitt| first2 = G.S | display-authors = 2 | title = Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group. |journal =Science | volume = 257|issue=5071 }}</ref> The validity of the taxon "Craniata" was further examined by Delarbre et al. (2002) using [[mtDNA]] [[DNA sequence|sequence]] data, concluding the Myxini are more closely related to [[Hyperoartia]] than to Gnathostomata – i.e., that modern jawless fishes form a clade called [[Cyclostomata]]. The argument is that if the Cyclostomata are indeed monophyletic, Vertebrata would return to its old content ([[Gnathostomata]] + [[Cyclostomata]]) and the name Craniata, being superfluous, would become a junior synonym.<ref name=r3/> Nowadays, molecular data are almost unanimously in consensus of cyclostome monophyly, with more recent work being directed at shared microRNA’s between cyclostomes and gnathostomes. <ref>{{cite journal| year=2010 |last1=Heimberg|first1=A.M| last2=Cowper-Sal| first2 = R | last3 = Semon | first3 = M | last4 = Donoghue | first4 = P.C | last5 = Peterson | first5 = K.J | display-authors = 1 | title = microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate. |journal =Proceedings of the National Academy of Sciences| volume = 107|issue=45 }}</ref> The current classification supported by molecular analyses (which show that lampreys and hagfishes are sister taxa), as well as the fact that hagfishes do, in fact, have rudimentary vertebrae places hagfishes in Cyclostomata.<ref name=":0" /> ==Phylogeny== The following hagfish and lamprey phylogeny is based on the work of Shigeru Kuratani and Shigehiro Kuraku<!-- citation -->. Figure summary: The phylogeny and timing of cyclostome diversification are illustrated so that branch lengths correspond to evolutionary times (black solid lines). Numeraical time scales corresponding to constraints sets I-III in this table are indicated in the upper rows. The geological time scale based on the char provided by the [[Geological Society of America]] (http://geosociety.org/science/timescale/timescl.htm) is added to the time scale based on constraint set I. Black circles indicate branching points whose divergence times were estimated in this study. The divergence time of the split between Myxininae and Eptatretinae and between Petromyzon and Lethenteron/Lampetra is based on both synonymous substitution clocks and amino acid-based relaxed clocks using mtDNA and nuDNA. The divergence time of the split between Myxiniformes and Petromyzontiformes is solely based on a relaxed clock analysis using amino acid sequences encoded by mtDNA and nuDNA. The divergence time of the split between Geotriinae and Petromyzoninae is estimate based on strict molecular clocks. <ref>{{cite journal| year=2006 |last1=Kuraku|first1=S| last2=Kuratani| first2 = S | display-authors = 2 | title = Time scale for cyclostome evolution inferred with a phylogenetic diagnosis of hagfish and lamprey cDNA sequencese. |journal = Zoological Sciences| volume = 23|issue=12 }}</ref> ==Commercial use== [[File:Korean cuisine-Kkomjangeo bokkeum-01.jpg|thumb|right|''Kkomjangeo bokkeum'' (꼼장어 볶음), Korean stir-fried fish dish made with the hagfish ''[[Eptatretus burgeri]]'']] ===As food=== Hagfish are not often eaten, owing to their repugnant looks and sliminess. However the [[inshore hagfish]], found in the Northwest Pacific,<ref>[http://www.fishbase.org/Summary/SpeciesSummary.php?id=8712 "Eptatretus burgeri, Inshore hagfish : fisheries, bait"]. ''FishBase''.</ref> is valued as food in [[Korea]]. The hagfish is kept alive and irritated by rattling its container with a stick, prompting it to produce slime in large quantities. This slime is used in a similar manner as egg whites in various forms of [[Korean cuisine|cookery]] in the region.{{Citation needed|date=December 2016}} The inshore hagfish, known as ''kkomjangeo'' (꼼장어) or ''meokjango'' (먹장어) in [[Korean language|Korean]] and ''nuta-unagi'' (ぬたうなぎ) in [[Japanese language|Japanese]], is the only member of the hagfish family with a seasonal reproductive cycle. ===Skins=== Hagfish skin, used in a variety of clothing accessories, is usually referred to as '''eel skin'''. It produces a particularly durable leather, especially suitable for wallets and belts.<ref>{{Cite news|url=http://www.fishermensnews.com/story/2013/02/01/features/slimed-ugly-hagfish-yields-somewhat-pretty-income/149.html|title=Slimed: Ugly Hagfish Yields Somewhat Pretty Income|last=Dillman|first=Terry|date=1 February 2013|work=Fishermen's News }}</ref> ==References== {{Reflist|28em}} ==Further reading== {{refbegin|28em}} *{{FishBase family|family=Myxinidae|year=2011|month=February}} *{{cite journal | last1=Bardack | first1=D | year=1991 | title=First fossil hagfish (Myxinoidea): a record from the Pennsylvanian of Illinois | journal=Science | volume=254 | issue=5032 | pages=701–703 | doi=10.1126/science.254.5032.701| pmid=17774799 }} *{{cite journal | last1=Bardack | first1=D. | last2=Richardson | first2=E. S. Jr | year=1977 | title=New agnathous fishes from the Pennsylvanian of Illinois | journal=Fieldiana |series=Geology | volume=33 | pages=489–510 | doi=10.5962/bhl.title.5167}} *Brodal, A. and Fänge, R. (ed.) (1963). The Biology of Myxine, Universitetsforlaget, Oslo. *{{cite journal | last1=Fernholm | first1=B. | last2=Holmberg | first2=K. | year=1975 | title=The eyes in three genera of hagfish (''Eptatretus'', ''Paramyxine'' and ''Myxine'') – A case of degenerative evolution | journal=Vision Research | volume=15 | issue=2 | pages=253–259 | doi=10.1016/0042-6989(75)90215-1| pmid=1129982 }} *Hardisty, M. W. (1982). Lampreys and hagfishes: Analysis of cyclostome relationships. In The Biology of Lampreys, (ed. M. W. Hardisty and I. C. Potter), Vol.4B, pp.&nbsp;165–259. Academic Press, London. *Janvier, P. (1996). Early vertebrates. Oxford Monographs in Geology and Geophysics, 33, Oxford University Press, Oxford. *{{cite book|last=Marinelli|first=Wilhelm|title=Vergleichende Anatomie und Morphologie der Wirbeltiere: 2. Lieferung. Myxine glutinosa (L.)|url={{google books|plainurl=y|id=FC2UjgEACAAJ}}|year=1956|publisher=Franz Deuticke}} *{{cite journal | last1=Yalden | first1=D.W. | year=1985 | title=Feeding mechanisms as evidence for cyclostome monophyly | journal=Zoological Journal of the Linnean Society | volume=84 | issue=3 | pages=291–300 | doi=10.1111/j.1096-3642.1985.tb01802.x}} *{{cite journal | last1=Stock | first1=D. W. | last2=Whitt | first2=G. S. | year=1992 | title=Evidence from 18S ribosomal RNA that lampreys and hagfishes form a natural group | journal=Science | volume=257 | issue=5071 | pages=787–789 | doi=10.1126/science.1496398 | pmid=1496398}} *{{cite journal |doi=10.1643/0045-8511(2006)6[225:ANSOGS]2.0.CO;2 |last1=Mincarone |first1=Michael M. |last2=Stewart |first2=Andrew L. |title=A new species of giant seven-gilled hagfish (Myxinidae: ''Eptatretus'') from New Zealand |journal=Copeia |volume=2006 |issue=2 |pages=225–229 |year=2006}} *{{cite book|editor=J.M. Jørgensen|editor2=J.P. Lomholt|editor3=R.E. Weber|editor4=H. Malte|title=The biology of hagfishes|location=London |publisher=[[Chapman & Hall]]|year=1997}} *{{cite journal|last=Delarbre |first=C |year=2002 |title=Complete Mitochondrial DNA of the Hagfish, ''Eptatretus burgeri'': The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly |journal=Molecular Phylogenetics and Evolution |volume=22 |issue=2 |pages=184–192 |doi=10.1006/mpev.2001.1045 |pmid=11820840|last2=Gallut|first2=C |last3=Barriel |first3=V|last4=Janvier |first4=P |last5=Gachelin |first5=G |displayauthors=1}} *{{cite journal |author=Bondareva |last2=Schmidt |first2=EE |last-author-amp=yes |date=November 2003 |title=Early Vertebrate Evolution of the TATA-Binding Protein, TBP |journal=Molecular Biology and Evolution |volume=20 |issue=11 |pages=1932–1939 |doi=10.1093/molbev/msg205 |pmid=12885957|pmc=2577151}} *Ewoldt, R. H., Winegard, T. M. and Fudge D. S. (2010). Non-linear viscoelasticity of hagfish slime. Int. J. Lin. Mech. 46: 627–636. *Fudge, D. (2001). [http://elibrary.ru/item.asp?id=4223151 ''Hagfishes: Champions of Slime''] Nature Australia, Spring 2001 ed., Australian Museum Trust, Sydney. pp.&nbsp;61–69. *{{cite journal | last1=Fudge | first1=D. S. | last2=Gardner | first2=K. H. | last3=Forsyth | first3=V. T. | last4=Riekel | first4=C. | last5=Gosline | first5=J. M. | year=2003 | title=The mechanical properties of hydrated intermediate filaments: Insights from hagfish gland thread cells | journal=Biophysical Journal | volume=85 | issue=3| pages=2015–2027 | pmc=1303373 | pmid=12944314 | doi=10.1016/S0006-3495(03)74629-3}} *{{cite journal | last1=Fudge | first1=D. S. | last2=Hillis | first2=S. | last3=Levy | first3=N. | last4=Gosline | first4=J. M. | year=2010 | title=Hagfish slime threads as a biomimetic model for high performance protein fibres | url=http://www.comparativephys.ca/system/files/Fudge_etal_Bioinspir%2526Biomim.pdf | format=PDF | journal=Bioinspiration & Biomimetics | volume=5 | pages=1–8 }}{{dead link|date=October 2017 |bot=InternetArchiveBot |fix-attempted=yes }} *{{cite journal | last1=Fudge | first1=D. S. | last2=Levy | first2=N. | last3=Chiu | first3=S. | last4=Gosline | first4=J. M. | year=2005 | title=Composition, morphology and mechanics of hagfish slime | url=http://jeb.biologists.org/content/208/24/4613.full | journal=Journal of Experimental Biology | volume=208 | issue=24| pages=4613–4625 | doi=10.1242/jeb.01963}} *{{cite journal | last1=Winegard | first1=T. M. | last2=Fudge | first2=D. S. | year=2010 | title=Deployment of hagfish slime thread skeins requires the transmission of mixing forces via mucin strands | url=http://jeb.biologists.org/content/213/8/1235.full | journal=Journal of Experimental Biology | volume=213 | issue=8| pages=1235–1240 | doi=10.1242/jeb.038075}} {{refend}} ==External links== {{Commons category|Myxinidae}} {{NIE Poster|year=1905|Hagfish}} *[http://www.fishbase.org/Summary/FamilySummary.cfm?ID=2 FishBase entry for Myxinidae] *[https://www.youtube.com/watch?v=NYRr_MrjebA YouTube 5+ minute video of Scripps scientist/diver on hagfish] *[http://www.metacafe.com/watch/1597296/hagfish_and_the_disgusting_slime/ Metacafe video of a University of Alberta grad student showing slime production of hagfish while in Bamfield, British Columbia] * [http://www.3news.co.nz/Beware-the-hagfish---repeller-of-sharks/tabid/1216/articleID/231051/Default.aspx Beware the hagfish – repeller of sharks] ''3 News'', 28 Oct 2011. Video. * [http://blog.tepapa.govt.nz/2011/10/28/hagfish-versus-sharks-1-0/ Hagfish versus sharks : 1-0] ''Te Papa Blog'', 28 October 2011. * [https://www.youtube.com/watch?v=nzMB8jqioV0 Teen Spots Hagfish-Slurping Elephant Seal – YouTube] (2:11) * [http://www.bbc.co.uk/news/magazine-21966514 What happens when a shark attacks a hagfish – BBC] (0:39) * [https://www.youtube.com/watch?v=pmaal7Hf0WA Vancouver Aquarium Hagfish Slime] {{Animalia}} {{Chordata}} {{Taxonbar|from=Q75713}} [[Category:Myxinidae| ]] [[Category:Marine edible fish]] [[Category:Fish of the Pacific Ocean]] [[Category:Scavengers]]'