Biology:Hagfish

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Short description: Family of eel-shaped, slime-producing animal

Hagfish
Temporal range: Late Carboniferous–Recent
Eptatretus hexatrema 15727711.jpg
Sixgill hagfish, Eptatretus hexatrema
Scientific classification e
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Agnatha
Superclass: Cyclostomi
Class: Myxini
Order: Myxiniformes
Family: Myxinidae
Rafinesque, 1815
Type species
Myxine glutinosa
Linnaeus, 1758
Genera[1]
Synonyms
  • Bdellostomatidae Gill, 1872
  • Homeidae Garman, 1899
  • Paramyxinidae Berg, 1940
  • Diporobranchia Latreille, 1825[2]

Hagfish, of the class Myxini /mɪkˈsaɪnaɪ/ (also known as Hyperotreti) and order Myxiniformes /mɪkˈsɪnɪfɔːrmiːz/, are eel-shaped jawless 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.[3] Hagfish are marine predators and scavengers. Hagfish defend themselves against predators by releasing copious amounts of slime from glands in their skin.[4]

Although their exact relationship to the only other living group of jawless fish, the lampreys, was long the subject of controversy, genetic evidence suggests that hagfish and lampreys are more closely related to each other than to jawed vertebrates, forming the clade Cyclostomi.[5] The oldest-known stem group hagfish are known from the Late Carboniferous, around 310 million years ago,[6] with modern representatives first being recorded in the mid-Cretaceous around 100 million years ago.[5]

Physical characteristics

Two views of the hagfish (Myxini glutinosa) with analytical overlays and dissection, published 1905

Body features

Hagfish are typically about 50 cm (19.7 in) in length. The largest-known species is Eptatretus goliath, with a specimen recorded at 127 cm (4 ft 2 in), while Myxine kuoi and Myxine pequenoi seem to reach no more than 18 cm (7.1 in). Some have been seen as small as 4 cm (1.6 in).[citation needed]

Hagfish have elongated, eel-like bodies, and paddle-like tails. The skin is naked and covers the body like a loosely fitting sock. They are generally a dull pink color and look quite worm-like. They have cartilaginous skulls (although the part surrounding the brain is composed primarily of a fibrous sheath) and tooth-like structures composed of keratin. Colors depend on the species, ranging from pink to blue-grey, and black or white spots may be present. Eyes are simple eyespots, not lensed 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.[7]

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

Its skin is attached to the body only 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.[8] The Atlantic hagfish, representative of the subfamily Myxininae, and the Pacific hagfish, representative of the subfamily Eptatretinae, differ in that the latter has muscle fibers embedded in the skin. The resting position of the Pacific hagfish also tends to be coiled, while that of the Atlantic hagfish is stretched.[9][10]

Slime

An Atlantic hagfish (Myxine glutinosa) using its slime to get away from a kitefin shark (Dalatias licha) and an Atlantic wreckfish (Polyprion americanus)
Pacific hagfish trying to hide under a rock

Hagfish can exude copious quantities of a milky and fibrous slime or mucus, from specialized slime glands.[4] When released in seawater, the slime expands to 10,000 times its original size in 0.4 seconds.[11] This slime that hagfish excrete has very thin fibers that make it more durable and retentive than the slime excreted by other animals.[12] The fibers are made of proteins and also make the slime flexible. If they are caught by a predator, they can quickly release a large amount of slime to escape.[13] If they remain captured, they can tie themselves in an overhand knot, and work their way from the head to the tail of the animal, scraping off the slime and freeing themselves from their captor. Rheological investigations showed that hagfish slime viscosity increases in elongational flow which favors gill clogging of suction feeding fish, while its viscosity decreases in shear which facilitates scraping off the slime by the travelling-knot.[14]

Recently, the slime was reported to entrain water in its keratin-like intermediate filaments excreted by gland thread cells, creating a slow-to-dissipate, viscoelastic substance, rather than a simple gel. It has been shown to impair the function of a predator fish's gills. In this case, the hagfish's mucus would clog the predator's gills, disabling their ability to respire. The predator would release the hagfish to avoid suffocation. Because of the mucus, few marine predators target the hagfish. Other predators of hagfish are varieties of birds or mammals.[15]

Free-swimming hagfish also slime when agitated, and later clear the mucus using the same travelling-knot behavior.[16][17] 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 thread keratin (EsTKα and EsTKγ; Q90501 and Q90502), the protein that make up its slime filaments, is under investigation as an alternative to spider silk for use in applications such as body armor.[18] These alpha-keratin proteins in hagfish slime transform from an α-helical structure to a stiffer β sheet structure when stretched.[19] With combined draw-processing (stretching) and chemical crosslinking, recombinant slime keratin turns into a very strong fiber with an elastic modulus reaching 20 GPa.[20]

When in 2017 a road accident on U.S. Highway 101 resulted in 7,500 pounds (3,400 kg) of hagfish being spilled, they emitted sufficient slime to cover the road and a nearby car.[21]

Respiration

A hagfish generally respires by taking in water through its pharynx, past the velar chamber, and bringing the water through the internal gill pouches, which can vary in number from five to 16 pairs, depending on species.[22] 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, as in lampreys.[23][24] The unidirectional water flow passing the gills is produced by rolling and unrolling velar folds located inside a chamber developed from the nasohypophyseal 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.[25] 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.[26] The skin has also been suggested to be capable of cutaneous respiration.[27]

Nervous system

Dorsal / left lateral views of dissected hagfish brain, scale bar added for size

The origins of the vertebrate nervous system are of considerable interest to evolutionary biologists, and cyclostomes (hagfish and lampreys) are an important group for answering this question. The complexity of the hagfish brain has been an issue of debate since the late 19th century, with some morphologists suggesting that they do not possess a cerebellum, while others suggest that it is continuous with the midbrain.[28] It is now considered that the hagfish neuroanatomy is similar to that of lampreys.[29] A common feature of both cyclostomes is the absence of myelin in neurons.[30] The brain of a hagfish has specific parts similar to the brains of other vertebrates.[31] The dorsal and ventral muscles located towards the side of the hagfish body are connected to spinal nerves. The spinal nerves that connect to the muscles of the pharyngeal wall grow individually to reach them.[32]

Eye

The hagfish eye lacks a lens, extraocular muscles, and the three motor cranial nerves (III, IV, and VI) found in more complex vertebrates, which is significant to the study of the evolution of more complex eyes. A parietal eye is also absent in extant hagfish.[33][34] 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.[7] Paleontological evidence suggests, however, that the hagfish eye is not plesiomorphic but rather degenerative, as fossils from the Carboniferous have revealed hagfish-like vertebrates with complex eyes. This would suggest that ancestrally Myxini possessed complex eyes.[35][36]

Cardiac function, circulation, and fluid balance

Hagfish are known to have one of the lowest blood pressures among the vertebrates.[37] One of the most primitive types of fluid balance found in animals is among these creatures; whenever a rise in extracellular fluid occurs, the blood pressure rises and this, in turn, is sensed by the kidney, which excretes excess fluid.[26] They also have the highest blood volume to body mass of any chordate, with 17 ml of blood per 100 g of mass.[38]

The hagfish circulatory system has been of considerable interest to evolutionary biologists and present day readers of physiology. Some observers first believed that the hagfish heart was not innervated (as the hearts of jawed vertebrates are),[39] but further investigation revealed that the hagfish does have a true innervated heart. The hagfish circulatory system also includes multiple accessory pumps throughout the body, which are considered auxiliary "hearts".[37]

Hagfish are the only known vertebrates with osmoregulation isosmotic to their external environment. Their renal function remains poorly described. There is a hypothesis that they excrete ions in bile salts.[40]

Musculoskeletal system

Hagfish musculature differs from jawed vertebrates in that they have neither a horizontal septum nor a vertical septum, which in jawed vertebrates are 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 their dental plate. In particular, hagfish muscles have increased force and gape size compared to similar-sized jawed vertebrates, but lack the speed amplification given by jawed vertebrates' muscles, suggesting that jaws are faster acting than hagfish dental plates.[41]

Vertical section of hagfish midline trunk: The notochord is the only skeletal element, and the musculature has no septum, neither horizontal nor vertical.
Hagfish skull Fig 74 in Kingsley 1912

The hagfish skeleton comprises the skull, the notochord, and the caudal fin rays. The first diagram of the hagfish endoskeleton was made by Frederick Cole in 1905.[42] In Cole's monograph, 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 plates) articulated with a series of large cartilage shafts. The nasal capsule is considerably expanded in hagfish, comprising a fibrous sheath lined with cartilage rings. In contrast to lampreys, the braincase is noncartilaginous. The role of their branchial arches is still highly speculative, as hagfish embryos undergo a caudal shift of the posterior pharyngeal pouches; thus, the branchial arches do not support gills.[43] While parts of the hagfish skull are thought to be homologous with lampreys, they are thought to have very few elements homologous with jawed vertebrates.[44]

Reproduction

Egg development in a female black hagfish, Eptatretus deani
Drawing of Eptatretus polytrema

Very little is known about hagfish reproduction. Obtaining embryos and observing reproductive behavior are difficult due to the deep-sea habitat of many hagfish species.[45] In the wild females outnumber males, with the exact sex-ratio differing depending on the species. E. burgeri, for example, has nearly a 1:1 ratio, while M. glutinosa females are significantly more common than males.[45] Some species of hagfish are sexually undifferentiated before maturation, and possess gonadal tissue for both ovaries and testis.[46] It has been suggested that females develop earlier than males, and that this may be the reason for unequal sex ratios. Hagfish testis are relatively small.[45]

Depending on species, females lay from one to 30 tough, yolky eggs. These tend to aggregate due to having Velcro-like tufts at either end.[45] It is unclear how hagfish go about laying eggs, although researchers have proposed three hypotheses based on observations of the low percentage of males and small testis. The hypotheses are that female hagfish lay eggs in small crevices in rock formations, the eggs are laid in burrow beneath the sand, and the slime produced by the hagfish is used to hold the eggs in a small area.[45] It is worth noting that no direct evidence has been found to support any of these hypotheses. Hagfish do not have a larval stage, in contrast to lampreys.[45]

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, and the proximal tubule of the nephron is also connected with the coelom, providing lubrication.[47] 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.

The hagfish embryo can develop for as long as 11 months before hatching, which is shorter in comparison to other jawless vertebrates.[48] Not much was known about hagfish embryology until recently, when husbandry advances enabled considerable insight into the group's evolutionary development. New insights into the evolution of neural crest cells, support the consensus that all vertebrates share these cells, which might be regulated by a common subset of genes.[49] Their genome has a large number of microchromosomes which are lost during the animal's development, leaving only the reproductive organs with a complete genome.[50] Hagfish possess gonadotropins which secrete from pituitary glands to the gonads to stimulate development.[51] This suggests that hagfish have an early version of the Hypothalamic–pituitary–gonadal axis, a system which once thought to be exclusive to the Gnathostomes.

Drawing of a New Zealand hagfish

Some species of hagfish reproduce seasonally, stimulated by hormones from their pituitary gland. E. burgeri is known to reproduce and migrate annually.[52]

Feeding

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 worms 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.[53] 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.[54]

Like leeches, they have a sluggish metabolism and can survive months between feedings;[55][56] their feeding behavior, however, appears quite vigorous. Analysis of the stomach content of several species has revealed a large variety of prey, including polychaetes, shrimp, hermit crabs, cephalopods, brittle stars, bony fishes, sharks, birds, and whale flesh.[57]

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.[58] They are also able to absorb nutrients directly through their skin.[59]

Hagfish have also been observed actively 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.[60]

Classification

Pacific hagfish resting on the ocean bottom, at 280 m depth off the Oregon coast

Originally, Myxine was included by Linnaeus (1758) in Vermes. The fossil hagfish Myxinikela siroka, from the Late Carboniferous of the United States, is the oldest-known member of the group. It is in some respects more similar to lampreys, but shows key autapomorphies of hagfish.[6] In recent years, hagfish have become of special interest for genetic analysis investigating the relationships among chordates. Their classification as agnathans places hagfish as elementary vertebrates in between invertebrates and gnathostomes. However, discussion has long occurred in scientific literature about whether the hagfish were even invertebrate. Using fossil data, paleontologists posited that lampreys are more closely 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.[61] Molecular evidence in the early 1990s first began suggesting that lampreys and hagfish were more closely related to each other than to gnathostomes.[62] The validity of the taxon "Craniata" was further examined by Delarbre et al. (2002) using mtDNA sequence data, concluding the Myxini are more closely related to the Hyperoartia than to the Gnathostomata—i.e., that modern jawless fishes form a clade called the 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.[63] Nowadays, molecular data are almost unanimously in consensus of cyclostome monophyly, with more recent work being directed at shared microRNAs between cyclostomes and gnathostomes.[64] 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, which places hagfishes in Cyclostomata.[3]

Phylogeny

Hagfish are in the group Cyclostomata which includes jawless fish. The group Cyclostomata is characterized by two significant characteristics; keratinous tooth plates and movement of postotic myomeres to the orbitals.[5] According to fossil record, Hagfish and lampreys have been estimated to have diverged from one another during the Paleozoic period.[5] An experiment used an estimation of synonymous and nonsynonymous substitutions for nucleotides and supplemented that data with pre-existing data into a clock that would calculate divergence times for the taxons Myxine and Eptatretus.[65] This data found that the lineage diverged around 93–28 Mya.[65] Hagfish are excluded from the subphylum Gnathostomata because of morphological characteristics including the Hagfish arched tongue.[31] Hagfish embryos have characteristics of Gnathostomes and may be plesiomorphic;[31] however, these characteristics drastically change morphologically as the Hagfish matures.[31] The following hagfish and lamprey phylogeny is an adaptation based on the 2019 work of Miyashita et al.[66]

 
 

†Haikouella

 
 
 
 

†Haikouichthys

 
 

†Myllokunmingia

 
 
 
 

†Metaspriggina

 
Vertebrata
 

Gnathostomata (jawed fish)

 
 
†Anaspida
 

†Cornovichthys

 
 
 
 

†Achanarella

 
 

†Ciderius

 
 
 
 

†Birkeniida

 
 
 

†Lasanius

 
 
 

†Euphanerops

 
 

†Jamoytius

 
 
 
 
 
 
 
 

†Pipiscius

 
 
 

†Euconodonta (conodonts)

 
Cyclostomi
 
 

†Myxinikela

 
Myxinoidea
 
 

†Tethymyxine tapirostrum

 
 
 

Rubicundus eos

 
 

Rubicundus lopheliae

 
 
 
 
 
 

Myxine glutinosa

 
 

Neomyxine biniplicata

 
 
 
 

Eptatretus stoutii

 
 
 

Eptatretus burgeri

 
 

"Paramyxine" spp.

 
 
 
 
(crown group)
 
 
 

†Gilpichthys

 
 
 
 

†Hardistiella

 
 

†Mayomyzon

 
 
 
 

†Myxineidus

 
 
 

†Priscomyzon

 
 
 

†Mesomyzon

 
Petromyzontiformes
 
 

Geotria australis

 
 

Mordacia mordax

 
 
 
 

Petromyzon marinus

 
 
 

Lampetra fluviatilis

 
 

Lethenteron camtschaticum

 
 
 
(crown group)
 
 
 
 
 
(crown group)
 
 
 
(crown group)
 
 
 

Commercial use

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

As food

In most of the world, hagfish are not often eaten. But in Korea, the hagfish is a valued food, where it is generally skinned, coated in spicy sauce, and grilled over charcoal or stir-fried. It is especially popular in the southern port cities of the peninsula, such as Busan and coastal cities in South Gyeongsang Province.[citation needed]

Due to their being eaten in Korea, most hagfish caught for food elsewhere in the world is fished with intent of being exported to South Korea . The inshore hagfish, found in the northwest Pacific, is eaten in Japan [67] and South Korea. As hagfish slime binds vast amounts of liquid even at low temperatures, it was proposed as an energy-saving alternative for the production of tofu that does not require heating.[68]

In textiles

The hagfish slime threads can be used as ultra-strong fiber for clothing. Douglas Fudge, of Chapman University, has conducted research in this area.[69][70]

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.[71]

References

  1. ↑ Nelson, Joseph S.; Grande, Terry C.; Wilson, Mark V. H. (2016). Fishes of the World (5th ed.). John Wiley & Sons. ISBN 9781118342336. 
  2. ↑ van der Laan, Richard; Eschmeyer, William N.; Fricke, Ronald (2014). "Family-group names of Recent fishes". Zootaxa 3882 (2): 001–230. doi:10.11646/zootaxa.3882.1.1. ISSN 1175-5326. PMID 25543675. 
  3. ↑ 3.0 3.1 Reece, Jane (2014). Campbell Biology. Boston: Pearson. pp. 717. ISBN 978-0321775658. 
  4. ↑ 4.0 4.1 Zeng, Yu; Plachetzki, David C; Nieders, Kristen; Campbell, Hannah; Cartee, Marissa; Pankey, M Sabrina; Guillen, Kennedy; Fudge, Douglas (2023-03-10). "Epidermal threads reveal the origin of hagfish slime" (in en). eLife 12. doi:10.7554/eLife.81405. ISSN 2050-084X. PMID 36897815. 
  5. ↑ 5.0 5.1 5.2 5.3 Miyashita, Tetsuto; Coates, Michael I.; Farrar, Robert; Larson, Peter; Manning, Phillip L.; Wogelius, Roy A.; Edwards, Nicholas P.; Anné, Jennifer et al. (2019-02-05). "Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny" (in en). Proceedings of the National Academy of Sciences 116 (6): 2146–2151. doi:10.1073/pnas.1814794116. ISSN 0027-8424. PMID 30670644. Bibcode: 2019PNAS..116.2146M. 
  6. ↑ 6.0 6.1 Miyashita, Tetsuto (23 November 2020). "A Paleozoic stem hagfish Myxinikela siroka — revised anatomy and implications for evolution of the living jawless vertebrate lineages" (in en). Canadian Journal of Zoology 98 (12): 850–865. doi:10.1139/cjz-2020-0046. ISSN 0008-4301. https://www.researchgate.net/publication/346740531. 
  7. ↑ 7.0 7.1 Hyperotreti . Tree of Life
  8. ↑ The world's fastest shark is no match for a sack of flaccid hagfish skin
  9. ↑ How the slimy hagfish ties itself up in knots—and survives shark attacks
  10. ↑ "Comparative Biomechanics of Hagfish Skins SICB - 2017 meeting - Abstract Details". http://www.sicb.org/meetings/2017/schedule/abstractdetails.php?id=391. 
  11. ↑ Here’s how hagfish slime gets 10,000 times bigger in 0.4 seconds
  12. ↑ Fudge, Douglas; Levy, Nimrod; Chiu, Scott; Gosline, John (2005). "Composition, morphology and mechanics of hagfish slime". Journal of Experimental Biology 208 (24): 4613–4625. doi:10.1242/jeb.01963. PMID 16326943. 
  13. ↑ Böni, Lukas; Fischer, Peter; Böcker, Lukas; Kuster, Simon; Rühs, Patrick (2016). "Hagfish slime and mucin flow properties and their implications for defense". Scientific Reports 6: 30371. doi:10.1038/srep30371. PMID 27460842. Bibcode: 2016NatSR...630371B. 
  14. ↑ Böni, Lukas; Fischer, Peter; Böcker, Lukas; Kuster, Simon; Rühs, Patrick A. (September 2016). "Hagfish slime and mucin flow properties and their implications for defense". Scientific Reports 6 (1): 30371. doi:10.1038/srep30371. PMID 27460842. Bibcode: 2016NatSR...630371B. 
  15. ↑ Lim, J; Fudge, DS; Levy, N; Gosline, JM (January 31, 2006). "Hagfish slime ecomechanics: testing the gill-clogging hypothesis". Journal of Experimental Biology 209 (Pt 4): 702–710. doi:10.1242/jeb.02067. PMID 16449564. 
  16. ↑ Martini, F. H. (1998). "The ecology of hagfishes". in Jørgensen, J. M.; Lomholt, J. P.; Weber, R. E. et al.. The Biology of Hagfishes. London: Chapman and Hall. pp. 57–77. ISBN 978-0-412-78530-6. https://books.google.com/books?id=vu1uzL0p7xsC&pg=PA57. 
  17. ↑ Strahan, R. (1963). "The behavior of myxinoids". Acta Zoologica 44 (1–2): 73–102. doi:10.1111/j.1463-6395.1963.tb00402.x. 
  18. ↑ "Slime from this 300 million-year-old creature could create bulletproof body armor" (in en-US). New York Post. 2017-10-25. https://nypost.com/2017/10/25/slime-from-this-300-million-year-old-creature-could-create-bulletproof-body-armor/. 
  19. ↑ Fu, Jing; Guerette, Paul A.; Miserez, Ali (8 July 2015). "Self-Assembly of Recombinant Hagfish Thread Keratins Amenable to a Strain-Induced α-Helix to β-Sheet Transition". Biomacromolecules 16 (8): 2327–2339. doi:10.1021/acs.biomac.5b00552. PMID 26102237. 
  20. ↑ Fu, Jing; Guerette, Paul A.; Pavesi, Andrea; Horbelt, Nils; Lim, Chwee Teck; Harrington, Matthew J.; Miserez, Ali (2017). "Artificial hagfish protein fibers with ultra-high and tunable stiffness". Nanoscale 9 (35): 12908–12915. doi:10.1039/c7nr02527k. PMID 28832693. 
  21. ↑ LeBlanc, Paul (14 July 2017). "Slime eels cause multiple car pileup on Oregon highway". https://amp.cnn.com/cnn/2017/07/14/us/slime-eels-highway-accident-oregon-trnd/index.html. 
  22. ↑ Springer, Joseph; Holley, Dennis (2012). An Introduction to Zoology. Jones & Bartlett Publishers. pp. 376–. ISBN 978-1-4496-9544-6. https://books.google.com/books?id=BzgNZca_L5AC&pg=PA376. 
  23. ↑ Hughes, George Morgan (1963). Comparative Physiology of Vertebrate Respiration. Harvard University Press. pp. 9–. ISBN 978-0-674-15250-2. https://archive.org/details/ost-biology-comparativephysi00hugh. 
  24. ↑ Wake, Marvalee H. (1992). Hyman's Comparative Vertebrate Anatomy. University of Chicago Press. pp. 81–. ISBN 978-0-226-87013-7. https://books.google.com/books?id=VKlWjdOkiMwC&pg=PA81. 
  25. ↑ Bone, Quentin; Moore, Richard (2008). Biology of Fishes. Taylor & Francis. pp. 128–. ISBN 978-1-134-18631-0. https://books.google.com/books?id=e2N4AgAAQBAJ&pg=PA128. 
  26. ↑ 26.0 26.1 Jørgensen, Jørgen Mørup (1998). The Biology of Hagfishes. Springer Science & Business Media. pp. 231–. ISBN 978-0-412-78530-6. https://books.google.com/books?id=vu1uzL0p7xsC&pg=PA231. 
  27. ↑ Helfman, Gene; Collette, Bruce B.; Facey, Douglas E.; Bowen, Brian W. (2009). The Diversity of Fishes: Biology, Evolution, and Ecology. John Wiley & Sons. pp. 235–. ISBN 978-1-4443-1190-7. https://books.google.com/books?id=FyehAR6hsUUC&pg=PA235. 
  28. ↑ Larsell, O (1947), "The cerebellum of myxinoids and petromyzonts including developmental stages in the lampreys.", Journal of Experimental Biology 210 (22): 3897–3909, doi:10.1002/cne.900860303, PMID 20239748 
  29. ↑ Wicht, H (1996), "The brains of lampreys and hagfishes: Characteristics, characters, and comparisons.", Brain, Behavior and Evolution 48 (5): 248–261, doi:10.1159/000113204, PMID 8932866 
  30. ↑ Bullock, T.H.; Moore, J.K.; Fields, R.D. (1984). "Evolution of myelin sheaths: both lamprey and hagfish lack myelin.". Neuroscience Letters 48 (2): 145–148. doi:10.1016/0304-3940(84)90010-7. PMID 6483278. 
  31. ↑ 31.0 31.1 31.2 31.3 Ota, Kinya; Kuratani, Shigeru (2008). "Developmental Biology of Hagfishes, with a Report on Newly Obtained Embryos of the Japanese Inshore Hagfish, Eptatretus burgeri". Zoological Science 25 (10): 999–1011. doi:10.2108/zsj.25.999. PMID 19267636. 
  32. ↑ Oisi, Yasuhiro; Fujimoto, Satoko; Ota, Kinya; Kuratani, Shigeru (2015). "On the peculiar morphology and development of the hypoglossal, glossopharyngeal and vagus nerves and hypobranchial muscles in the hagfish". Zoological Letters 1 (6): 6. doi:10.1186/s40851-014-0005-9. PMID 26605051. 
  33. ↑ Ostrander, Gary Kent (2000). The Laboratory Fish. Elsevier. pp. 129–. ISBN 978-0-12-529650-2. https://books.google.com/books?id=Hp4YSFiSD0IC&pg=PT129. 
  34. ↑ "Keeping an eye on evolution". PhysOrg.com. 2007-12-03. http://www.physorg.com/news115919015.html. 
  35. ↑ Gabbott, S.E; Donoghu, P.C et al. (2016), "Pigmented anatomy in Carboniferous cyclostomes and the evolution of the vertebrate eye.", Proc. R. Soc. B 283 (1836): 20161151, doi:10.1098/rspb.2016.1151, PMID 27488650 
  36. ↑ Bardack, D (1991), "First fossil hagfish (Myxinoidea): a record from the Pennsylvanian of Illinois", Science 254 (5032): 701–3, doi:10.1126/science.254.5032.701, PMID 17774799, Bibcode: 1991Sci...254..701B 
  37. ↑ 37.0 37.1 Forster, Malcolm E.; Axelsson, Michael; Farrell, Anthony P.; Nilsson, Stefan (1991-07-01). "Cardiac function and circulation in hagfishes". Canadian Journal of Zoology 69 (7): 1985–1992. doi:10.1139/z91-277. ISSN 0008-4301. 
  38. ↑ Hagfish - Cronodon
  39. ↑ Jensen, D (1965), "The aneural heart of the hagfish.", Annals of the New York Academy of Sciences 127 (1): 443–58, doi:10.1111/j.1749-6632.1965.tb49418.x, PMID 5217274, Bibcode: 1965NYASA.127..443J 
  40. ↑ Robertson, J.D (1976), "Chemical composition of the body fluids and muscle of the hagfish Myxine glutinosa and the rabbit-fish Chimaera monstros.", Journal of Zoology 178 (2): 261–277, doi:10.1111/j.1469-7998.1976.tb06012.x 
  41. ↑ Clark, A.J.; Summers, A.P. (2007). "Morphology and kinematics of feeding in hagfish: possible functional advantages of jaws.". Journal of Experimental Biology 210 (22): 3897–3909. doi:10.1242/jeb.006940. PMID 17981857. 
  42. ↑ Cole, F.J. (1906), "A Monograph on the general Morphology of the Myxinoid Fishes, based on a study of Myxine. Part I. The Anatomy of the Skeleton.", Earth and Environmental Science Transactions of the Royal Society of Edinburgh 41 (3) 
  43. ↑ Oisi, Y.; Fujimoto, S.; Ota, K.G.; Kuratani, S. (2015). "On the peculiar morphology and development of the hypoglossal, glossopharyngeal and vagus nerves and hypobranchial muscles in the hagfish.". Zoological Letters 1 (1): 6. doi:10.1186/s40851-014-0005-9. PMID 26605051. 
  44. ↑ Oisi, Y.; Ota, K.G.; Fujimoto, S.; Kuratani, S. (2013). "Development of the chondrocranium in hagfishes, with special reference to the early evolution of vertebrates". Zoological Science 30 (11): 944–961. doi:10.2108/zsj.30.944. PMID 24199860. 
  45. ↑ 45.0 45.1 45.2 45.3 45.4 45.5 Ota, Kinya G.; Kuratani, Shigeru (2006). "The History of Scientific Endeavors Towards Understanding Hagfish Embryology". Zoological Science 23 (5): 403–418. doi:10.2108/zsj.23.403. ISSN 0289-0003. PMID 16766859. 
  46. ↑ Martini, Frederic H.; Beulig, Alfred (2013-11-08). "Morphometics and Gonadal Development of the Hagfish Eptatretus cirrhatus in New Zealand" (in en). PLOS ONE 8 (11): e78740. doi:10.1371/journal.pone.0078740. ISSN 1932-6203. PMID 24250811. Bibcode: 2013PLoSO...878740M. 
  47. ↑ Kardong, Kenneth V. (2019). Vertebrates: comparative anatomy, function, evolution (Eighth ed.). New York. ISBN 978-1-259-70091-0. OCLC 1053847969. 
  48. ↑ Gorbman, A (1997). "Hagfish development". Zoological Science 14 (3): 375–390. doi:10.2108/zsj.14.375. 
  49. ↑ Ota, K.G; Kuraku, S.; Kuratani, S. (2007). "Hagfish embryology with reference to the evolution of the neural crest". Nature 446 (7136): 672–5. doi:10.1038/nature05633. PMID 17377535. Bibcode: 2007Natur.446..672O. 
  50. ↑ First genome of slime eels uncovers the deep evolutionary history of our genomes and bodies
  51. ↑ Nozaki, Masumi (2013). "Hypothalamic-Pituitary-Gonadal Endocrine System in the Hagfish" (in English). Frontiers in Endocrinology 4: 200. doi:10.3389/fendo.2013.00200. ISSN 1664-2392. PMID 24416029. 
  52. ↑ Powell, Mickie L.; Kavanaugh, Scott I.; Sower, Stacia A. (2005-01-01). "Current Knowledge of Hagfish Reproduction: Implications for Fisheries Management" (in en). Integrative and Comparative Biology 45 (1): 158–165. doi:10.1093/icb/45.1.158. ISSN 1540-7063. PMID 21676757. https://academic.oup.com/icb/article/45/1/158/604629. 
  53. ↑ Wilson, Hugh (November 2009) Hagfish – World's weirdest animals. green.ca.msn.com
  54. ↑ Glover, CN; Bucking, C; Wood, CM (2011-03-02). "Adaptations to in situ feeding: novel nutrient acquisition pathways in an ancient vertebrate". Proceedings of the Royal Society B: Biological Sciences 278 (1721): 3096–101. doi:10.1098/rspb.2010.2784. PMID 21367787. 
  55. ↑ "Introduction to the Myxini". Berkeley.edu website. http://www.ucmp.berkeley.edu/vertebrates/basalfish/myxini.html. 
  56. ↑ Lesser, M; Martini, Frederic H.; Heiser, John B. (3 January 1997). "Ecology of the hagfish, Myxine glutinosa L. in the Gulf of Maine I. Metabolic rates and energetics". Journal of Experimental Marine Biology and Ecology 208 (1–2): 215–225. doi:10.1016/S0022-0981(96)02665-2. 
  57. ↑ Zintzen, V.; Rogers, K. M.; Roberts, C. D.; Stewart, A. L.; Anderson, M. J. (2013). "Hagfish feeding habits along a depth gradient inferred from stable isotopes". Marine Ecology Progress Series 485: 223–234. doi:10.3354/meps10341. Bibcode: 2013MEPS..485..223Z. https://www.int-res.com/articles/meps_oa/m485p223.pdf. 
  58. ↑ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  59. ↑ Hagfish Just Got More Disgusting
  60. ↑ Zintzen, V.; Roberts, C. D.; Anderson, M. J.; Stewart, A. L.; Struthers, C. D.; Harvey, E. S. (2011). "Hagfish predatory behaviour and slime defence mechanism". Scientific Reports 1: 131. doi:10.1038/srep00131. PMID 22355648. Bibcode: 2011NatSR...1E.131Z. 
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  62. ↑ Stock, D.W.; Whitt, G.S. (1992). "Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group.". Science 257 (5071): 787–9. doi:10.1126/science.1496398. PMID 1496398. Bibcode: 1992Sci...257..787S. 
  63. ↑ Janvier, P. (2010). "MicroRNAs revive old views about jawless vertebrate divergence and evolution". Proceedings of the National Academy of Sciences 107 (45): 19137–19138. doi:10.1073/pnas.1014583107. PMID 21041649. Bibcode: 2010PNAS..10719137J. "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". 
  64. ↑ Heimberg, A.M et al. (2010). "microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate.". Proceedings of the National Academy of Sciences 107 (45): 19379–83. doi:10.1073/pnas.1010350107. PMID 20959416. 
  65. ↑ 65.0 65.1 Kuraku, S.; Kuratani, S. (2006). "Time scale for cyclostome evolution inferred with a phylogenetic diagnosis of hagfish and lamprey cDNA sequences". Zoological Science 23 (12): 1053–1064. doi:10.2108/zsj.23.1053. PMID 17261918. 
  66. ↑ Miyashita, Tetsuto; Coates, Michael I.; Farrar, Robert; Larson, Peter; Manning, Phillip L.; Wogelius, Roy A.; Edwards, Nicholas P.; Anné, Jennifer et al. (2019-02-05). "Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny" (in en). Proceedings of the National Academy of Sciences 116 (6): 2146–2151. doi:10.1073/pnas.1814794116. ISSN 0027-8424. PMID 30670644. Bibcode: 2019PNAS..116.2146M. 
  67. ↑ Froese, Rainer. "Epatretus burgeri Inshore hagfish". https://www.fishbase.se/summary/8712. 
  68. ↑ Böni, Lukas; Rühs, Patrick A.; Windhab, Erich J.; Fischer, Peter; Kuster, Simon (25 January 2016). "Gelation of Soy Milk with Hagfish Exudate Creates a Flocculated and Fibrous Emulsion- and Particle Gel". PLOS ONE 11 (1): e0147022. doi:10.1371/journal.pone.0147022. PMID 26808048. Bibcode: 2016PLoSO..1147022B. 
  69. ↑ Say hello to fish slime bulletproof vests
  70. ↑ "Guelph Researchers Solve Part of Hagfish Slime Mystery". 2014-04-04. https://www.uoguelph.ca/news/2014/04/guelph_research.html. 
  71. ↑ Dillman, Terry (1 February 2013). "Slimed: Ugly Hagfish Yields Somewhat Pretty Income". Fishermen's News. http://www.fishermensnews.com/story/2013/02/01/features/slimed-ugly-hagfish-yields-somewhat-pretty-income/149.html. 

Further reading

External links

Wikidata ☰ Q75713 entry



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