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Hagfish
Pacific hagfish resting on bottom
280 m depth off Oregon coast
Scientific classification
Kingdom: Animalia
Phylum: Chordata
(unranked): Craniata
Class: Myxini
Order: Myxiniformes
Family: Myxinidae
Genera

Eptatretus
Myxine
Nemamyxine
Neomyxine
Notomyxine
Paramyxine
Quadratus

Hagfish are marine craniates of the class Agnatha or Myxini, also known as Hyperotreti. Some researcher regard Myxini as not belonging to the subphylum Vertebrata.[1] That is, they are the only animals that have a skull but not a vertebral column.

Despite their name, there is some debate about whether they are strictly fish (as there is for lampreys), since they belong to a much more primitive lineage than any other group that is placed in the category of fish (Chondrichthyes and Osteichthyes). The earliest fossil record dates back approximately 330 million years to the Late Carboniferous period.[2]

Their unusual feeding habits and slime-producing capabilities have led members of the scientific and popular media to dub the hagfish as the most "disgusting" of all sea creatures.[3][4][5] Although hagfish are sometimes called "slime eels," they are not eels at all.[6]

Contents

Physical characteristics

Body features

Hagfish average about half a meter (18 in) long; The largest known species is Eptatretus goliath with a specimen recorded at 127 cm, while Myxine kuoi and Myxine pequenoi seem to reach no more than 18 cm.

Hagfish have elongated, eel-like bodies (so flexible they sometimes tie themselves in knots). They have four hearts, two brains, and a paddle-like tail.[7] They have cartilaginous skulls (although the part surrounding the brain is composed primarily of a fibrous sheath) and tooth-like structures composed of keratin. Colours depend on the species, ranging from pink to blue-grey, and black or white spots may be present. Eyes are simple eyespots, not compound eyes that can resolve images. Hagfish have no true fins and have six or eight barbels around the mouth and a single nostril. Instead of vertically articulating jaws like Gnathostomata (vertebrates with jaws), they have a pair of 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.[8]

Slime (and behavior)

Pacific hagfish trying to hide under a rock

Hagfish are long and vermiform, and can exude copious quantities of a slime or mucus (from which the typical species Myxine glutinosa was named) of unusual composition. When captured and held e.g. by the tail, they secrete the microfibrous slime, which expands into a gelatinous and sticky goo when combined with water; 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, as well as the slime. It has been conjectured that this singular behavior assists them in extricating themselves from the jaws of predatory fish or from the interior of their own "prey", and that the "sliming" might act as a distraction to predators.

Recently, though, it has been reported that the slime entrains water in its microfilaments, creating a slow-to-dissipate viscoelastic substance, rather than a simple gel, and it has been proposed that the primary protective effect of the slime is related to impairment of the function of a predator fish's gills.[9] Reportedly, most (all?) of the known predators of hagfish are birds or mammals, which could lend weight to the "gill-clogging hypothesis" as a highly successful evolutionary strategy tuned specifically to predatory fish.[10]

Free-swimming hagfish also "slime" when agitated and will later clear the mucus off by way of the same traveling-knot behavior.[11][12] The reported gill-clogging effect suggests that the traveling-knot behavior is useful or even necessary to restore the hagfish's own gill function after "sliming".

An adult hagfish can secrete enough slime to turn a 20 litre bucket of water into slime in a matter of minutes.[13]

Research is ongoing regarding the properties and possible applications of the components of hagfish slime filament protein.

Eye

In December 2003, an article was published by the University of Queensland claiming the hagfish's eye, which lacks both lens and extrinsic musculature, as being significant to the evolution of more complex eyes.[14] Hagfish eyespots when present can detect light, but as far as is known none can resolve detailed images. In Myxine and Neomyxine, the eyes are partly covered by the trunk musculature.[15]

Reproduction and the Urogenital System

Drawing of eptatretus minor
Drawing of a New Zealand hagfish.

Very little is known about hagfish reproduction. 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 it is thought that the ovary remains non-functional until the individual has reached a particular age or encounters a particular environmental stress. These two factors in combination suggest that the survival rate of hagfish is quite high.

Depending on species, females lay from one or two, to 20 to 30 tough, yolky eggs. These tend to aggregate due to having Velcro-like tufts at either end. Hagfish are sometimes seen curled around small clutches of eggs. It is not certain if this constitutes actual brooding behavior.

Hagfish do not have a larval stage, in contrast to lampreys, which have a long larval phase.

Hagfish have a mesonephric kidney and are often neotenic of their 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.

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 region, whereby they find an opening in the digestive system.

Feeding

Pacific hagfish at 150 meters depth, California, Cordell Bank National Marine Sanctuary.

While polychaete marine worms on or near the sea floor are a major source of nutrition, 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 victims from the inside[16]

Like leeches, they have a sluggish metabolism and can survive months between feedings.[17][18] But their feeding behavior appears, by contrast, quite vigorous.

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 hunks of flesh from carrion fish or cetaceans, eventually making an opening to permit entry to the interior of the body cavity of larger carcasses. It is to be expected that a healthy larger sea creature would be able to outfight or outswim this sort of assault.

However, 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 sealife makes easy prey for them.

The digestive tract of the hagfish is unique among the vertebrates because the food in the gut is enclosed in a permeable membrane, analogous to the peritrophic matrix of insects.[19]

Gastronomy

Kkomjangeo bokkeum (꼼장어 볶음), Korean stir-fried fish dish made with the hagfish Eptatretus burgeri.

Hagfish are usually not eaten owing to their repugnant looks, as well as their viscosity and unpleasant habits. However, a particular species, the inshore hagfish, found in the Northwest Pacific,[20] is valued as food in the Korean Peninsula.

The inshore hagfish, known as kkomjangeo (꼼장어) or meokjango (먹장어) in Korean and Nuta-unagi in Japanese, is the only member of the hagfish family having a seasonal reproductive cycle.

Genetic analysis

In recent years hagfish have become of special interest for genetic analysis investigating the relationships among chordates.

Classification

There has been long discussion in scientific literature about the hagfish being non-vertebrate. Given their classification as Agnatha, Hagfish are seen as an elementary vertebrate in between Prevertebrate and Gnathostome. Recent molecular biology analyses tend to classify hagfish as invertebrates (see references) within subphylum Craniata, because of their short molecular evolutionary distance from Vertebrata (sensu stricto). A single fossil of hagfish shows that there has been little evolutionary change in the last 300 million years.[21]

Genera

About 60 species are known, in 5 genera. A number of the species have only been recently discovered, living at depths of several hundred metres.

Eptatretus
  • Eptatretus bischoffii (Schneider, 1880)
  • Eptatretus burgeri (Girard, 1855), Inshore hagfish
  • Eptatretus caribbeaus Fernholm, 1982
  • Eptatretus carlhubbsi (McMillan and Wisner, 1984)
  • Eptatretus chinensis Kuo and Mok, 1994
  • Eptatretus cirrhatus (Forster, 1801), New Zealand hagfish
  • Eptatretus deani (Evermann & Goldsborough, 1907), Black hagfish
  • Eptatretus eos Fernholm, 1991
  • Eptatretus fernholmi McMillan & Wisner, 2004
  • Eptatretus fritzi Wisner & McMillan, 1990, Guadalupe hagfish
  • Eptatretus goliath Mincarone & Stewart, 2006
  • Eptatretus grouseri McMillan, 1999
  • Eptatretus hexatrema (Müller, 1836), Sixgill hagfish
  • Eptatretus indrambaryai Wongratana, 1983
  • Eptatretus lakeside Mincarone & McCosker, 2004
  • Eptatretus laurahubbsae McMillan and Wisner, 1984
  • Eptatretus longipinnis Strahan, 1975
  • Eptatretus lopheliae Fernholm & Quattrini, 2008
  • Eptatretus mcconnaugheyi Wisner & McMillan, 1990, Shorthead hagfish
  • Eptatretus mccoskeri McMillan, 1999
  • Eptatretus mendozai Hensley, 1985
  • Eptatretus menezesi Mincarone, 2000
  • Eptatretus minor Fernholm and Hubbs, 1981
  • Eptatretus multidens Fernholm and Hubbs, 1981
  • Eptatretus nanii Wisner and McMillan, 1988
  • Eptatretus octatrema (Barnard, 1923), Eightgill hagfish
  • Eptatretus okinoseanus (Dean, 1904)
  • Eptatretus polytrema (Girard, 1855), Fourteen-gill hagfish
  • Eptatretus profundus (Barnard, 1923), Fivegill hagfish
  • Eptatretus sinus Wisner & McMillan, 1990, Cortez hagfish
  • Eptatretus springeri (Bigelow & Schroeder, 1952), Gulf hagfish
  • Eptatretus stoutii (Lockington, 1878), Pacific hagfish
  • Eptatretus strahani McMillan and Wisner, 1984
  • Eptatretus strickrotti Møller & Jones, 2007
  • Eptatretus wisneri McMillan, 1999
Myxine
  • Myxine affinis Günther, 1870, Patagonian hagfish
  • Myxine australis Jenyns, 1842[22], Southern hagfish
  • Myxine capensis Regan, 1913, Cape hagfish
  • Myxine circifrons Garman, 1899, Whiteface hagfish
  • Myxine debueni Wisner & McMillan, 1995
  • Myxine dorsum Wisner & McMillan, 1995
  • Myxine fernholmi Wisner & McMillan, 1995
  • Myxine formosana Mok & Kuo, 2001
  • Myxine garmani Jordan & Snyder, 1901
  • Myxine glutinosa Linnaeus, 1758, Hagfish (or Atlantic hagfish)
  • Myxine hubbsi Wisner & McMillan, 1995
  • Myxine hubbsoides Wisner & McMillan, 1995
  • Myxine ios Fernholm, 1981, White-headed hagfish
  • Myxine jespersenae Møller, Feld, Poulsen, Thomsen & Thormar, 2005
  • Myxine knappi Wisner & McMillan, 1995)
  • Myxine kuoi Mok, 2002
  • Myxine limosa Girard, 1859
  • Myxine mccoskeri Wisner & McMillan, 1995
  • Myxine mcmillanae Hensley, 1991
  • Myxine paucidens Regan, 1913
  • Myxine pequenoi Wisner & McMillan, 1995
  • Myxine robinsorum Wisner & McMillan, 1995
  • Myxine sotoi Mincarone, 2001
Nemamyxine
  • Nemamyxine elongata Richardson, 1958
  • Nemamyxine kreffti McMillan and Wisner, 1982
Neomyxine
  • Neomyxine biniplicata (Richardson and Jowett, 1951)
Notomyxine
  • Notomyxine tridentiger (Garman, 1899)
Paramyxine
  • Paramyxine atami Dean, 1904
  • Paramyxine cheni Shen and Tao, 1975
  • Paramyxine fernholmi Kuo, Huang and Mok, 1994
  • Paramyxine moki McMillan & Wisner, 2004
  • Paramyxine sheni Kuo, Huang and Mok, 1994
  • Paramyxine walkeri McMillan & Wisner, 2004
  • Paramyxine wayuu Mok, Saavedra-Diaz & Acero P., 2001
  • Paramyxine wisneri Kuo, Huang and Mok, 1994
Quadratus
  • Quadratus ancon Mok, Saavedra-Diaz and Acero P., 2001
  • Quadratus nelsoni (Kuo, Huang and Mok, 1994)
  • Quadratus taiwanae (Shen and Tao, 1975)
  • Quadratus yangi (Teng, 1958)

Notes

  1. ^ N. A. Campbell and J. B. Reece (2005). Biology Seventh Edition. Benjamin Cummings, San Francisco CA.
  2. ^ http://tolweb.org/Hyperotreti
  3. ^ "Friends of Oceanography Public Lecture Series - Explores the Strange, Wondrous, and Disgusting Hagfish". University of Rhode Island. 2002-03-25. http://www.uri.edu/news/releases/html/02-0325-01.html. Retrieved 2008-02-19.  
  4. ^ "Slimy, disgusting and useful". Norwegian University of Science and Technology. http://www.ntnu.no/gemini/2003-06e/26-27.htm. Retrieved 2008-02-19.  
  5. ^ Frank, Tammy (2004-08-09). "Disgusting Hagfish and Magnificent Sharks". NOAA Ocean Explorer. http://oceanexplorer.noaa.gov/explorations/04deepscope/logs/aug9/aug9.html. Retrieved 2008-02-19.  
  6. ^ Sea and Sky: Atlantic Hagfish
  7. ^ Aird WC (2007) Endothelial biomedicine p. 67. Cambridge University Press. ISBN 9780521853767
  8. ^ http://tolweb.org/Hyperotreti
  9. ^ "Hagfish slime ecomechanics: testing the gill-clogging hypothesis". Journal of Experimental Biology 209, 702-710 (2006). January 31, 2006. http://jeb.biologists.org/cgi/content/full/209/4/702. Retrieved 2009-01-25.  
  10. ^ ibid.
  11. ^ "Martini, F. H. (1998). The ecology of hagfishes. The Biology of Hagfishes (ed. J. M. Jorgensen, J. P. Lomholt, R. E. Weber and H. Malte), pp. 57-77. London: Chapman and Hall.", The Biology of Hagfishes (ed. J. M. Jorgensen, J. P. Lomholt, R. E. Weber and H. Malte), pp. 57-77. London: Chapman and Hall.  
  12. ^ "Strahan, R. (1963). The behavior of myxinoids. Acta Zool. 44, 73-102.", Acta Zool. 44, 73-102.  
  13. ^ "Snotties at Southern Encounter". Southern Encounter Aquarium and Kiwi House. 2007-10-30. http://www.southernencounter.co.nz/seanews_whatsnew.htm. Retrieved 2008-10-30.  
  14. ^ "Keeping an eye on evolution". PhysOrg.com. 2007-12-03. http://www.physorg.com/news115919015.html. Retrieved 2007-12-04.  
  15. ^ Hyperotreti - Hagfishes
  16. ^ Hagfish - World's weirdest animals
  17. ^ "Introduction to the Myxini". Berkeley.edu website. http://www.ucmp.berkeley.edu/vertebrates/basalfish/myxini.html. Retrieved 2009-01-25.  
  18. ^ "Ecology of the hagfish, Myxine glutinosa L. in the Gulf of Maine I. Metabolic rates and energetics". Journal of Experimental Marine Biology and Ecology Volume 208, Issues 1-2, 3 January 1997, Pages 215-225. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T8F-3RHM81K-1J&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=c7bcfd4d06311041c96398a67b618314. Retrieved 2009-01-25.  
  19. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  20. ^ Fishbase - Eptatretus burgeri
  21. ^ "Myxinidae Information". Mudminnow Information Services. http://www.networksplus.net/maxmush/myxinidae.html. Retrieved 2010-8-5.  
  22. ^ First record of the Southern hagfish Myxine australis in Brazilian waters

References

Further reading

  • Bardack, D. (1991). First fossil hagfish (Myxinoidea): a record from the Pennsylvanian of Illinois. Science, 254, 701-703.
  • Bardack, D., and Richardson, E. S. Jr. (1977). New agnathous fishes from the Pennsylvanian of Illinois. Fieldiana: Geology, 33, 489-510.
  • Brodal, A. and Fänge, R. (ed.) (1963). The Biology of Myxine, Universitetsforlaget, Oslo.
  • Fernholm, B. and Holmberg, K. (1975). The eyes in three genera of hagfish (Eptatretus, Paramyxine and Myxine) - A case of degenerative evolution. Vision Research, 15, 253-259.
  • 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. 165-259. Academic Press, London.
  • Janvier, P. (1996). Early vertebrates. Oxford Monographs in Geology and Geophysics, 33, Oxford University Press, Oxford.
  • Marinelli, W. and Strenger, A. (1956). Vergleichende Anatomie und Morphologie der Wirberltiere. Myxine glutinosa. Franz Deuticke, Vienna.
  • Yalden, D.W. (1985). Feeding mechanisms as evidence for cyclostome monophyly. Zoological Journal of the Linnean Society. 84, 291-300.
  • Stock, D. W. and Whitt, G. S. (1992). Evidence from 18S ribosomal RNA that lampreys and hagfishes form a natural group. Science, 257, 787-789.

External links


Simple English

Hagfish
Scientific classification
Kingdom: Animalia
Phylum: Chordata
(unranked) Craniata
Class: Myxini
Order: Myxiniformes
Family: Myxinidae
Genera

Eptatretus
Myxine
Nemamyxine
Neomyxine
Notomyxine
Paramyxine
Quadratus

Hagfish are craniata in the class Agnatha or Myxini, also known as Hyperotreti. Even though fish are supposed to have backbones, hagfish do not.[1] Because of this, many researchers think Myxini should not be in the subphylum Vertebrata.[2] Their skeleton is made up of its skull, which is made out of cartilage.[1] However, because of its fins and gills, they are called fish.[1]

Contents

Feeding

Hagfish have "teeth" on their tongue to bite pieces of flesh from its prey, so they use their tongue teeth to eat.[1] Hagfish are scavengers. Its teeth pinch together to lock onto its food, helping it tear into the flesh of dead and dying fish which have sunk to the bottom of the sea, where it lives. Often, a hagfish will actually bore into the dead fish that it is eating, removing the insides of the dead fish.[1]

Usually, hagfish are only seen by men when nets that sweep the sea floor are pulled up. Every fish, even the dead ones at the bottom of the sea, are brought up into the boat by the net. In some of those dead fish, hagfish are found eating. The smelly fish are dumped onto the deck of ships with the hagfish poking out from their bodies.[1] When the hagfish becomes frightened at being taken off from the fish, they vomit up lots of slime. They vomit up enough slime to completely fill a two-gallon bucket.[1] The reason such a small fish can make more slime than it seems its small body can hold is because the slime comes out in fibrous strings that quickly swell up much bigger than they were at first when they are released from the hagfish's body.[1] Their unusual way of eating and sliminess has made many people call the hagfish the most "disgusting" of all sea creatures.[3][4][5] Although hagfish are sometimes called "slime eels," they are not eels at all.[6]

Description

File:Korean cuisine-Kkomjangeo
Kkomjangeo bokkeum (꼼장어 볶음), Korean stir-fried fish dish made with the hagfish Eptatretus burgeri.

Hagfish are usually about half a meter (18 in) long. They have long, eel-like bodies. Hagfish's eyes are small and not very useful, because the hagfish uses mostly its senses of smell and touch to find food. They have four hearts, two brains, and no backbone.[7][8] Because they do not have a backbone, hagfish can tie itself into a knot and slip out of that knot.[1] There are two reasons why hagfish do this. Hagfish makes a slime covering that makes predators go away. Lots of things, such as the insides of a dead fish, can stick onto the slime. When a hagfish ties itself into a knot and slips out, the slime is rubbed clean.[1] The second reason is for when it is eating.[1] Sometimes, to tear off a bit of food from a dead fish, the hagfish needs to pull very hard. Tying itself in a knot helps hagfish do this.[1]

Hagfish dish

Hagfish are usually not eaten by humans. However, inshore hagfish, known as kkomjangeo (꼼장어) or meokjango (먹장어) in Korean and Nuta-unagi in Japanese, is eaten in Korea.

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Fulbright, Jeannie K. (2006). Exploring Creation with Zoology 2: Swimming Creatures of the Fifth Day. 1106 Meridian Plaza, Suite 220, Anderson, IN 46016: Apologia Educational Ministries, Inc.. ISBN 1-932012-73-7. 
  2. Neil A. Campbell and J. B. Reece (2005). Biology Seventh Edition. Benjamin Cummings, San Francisco CA.
  3. "Friends of Oceanography Public Lecture Series - Explores the Strange, Wondrous, and Disgusting Hagfish". University of Rhode Island. 2002-03-25. http://www.uri.edu/news/releases/html/02-0325-01.html. Retrieved 2008-02-19. 
  4. "Slimy, disgusting and useful". Norwegian University of Science and Technology. http://www.ntnu.no/gemini/2003-06e/26-27.htm. Retrieved 2008-02-19. 
  5. Frank, Tammy (2004-08-09). "Disgusting Hagfish and Magnificent Sharks". NOAA Ocean Explorer. http://oceanexplorer.noaa.gov/explorations/04deepscope/logs/aug9/aug9.html. Retrieved 2008-02-19. 
  6. Sea and Sky: Atlantic Hagfish
  7. Aird WC (2007) Endothelial biomedicine p. 67. Cambridge University Press. ISBN 9780521853767
  8. Scholasticus K. "Hagfish Anatomy". Buzzle.com. http://www.buzzle.com/articles/hagfish-anatomy.html. Retrieved 10 March 2010. 

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