Hagfish

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Hagfish

Hagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade

Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
Craniata that does not also belong to the subphylum

Phylum

A phylum "Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states. is a taxonomic rank below Kingdom and above Class ....
Vertebrata. That is, they are the only animals which have a skull

Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
but not a vertebral column

Vertebral column

In human anatomy, the vertebral column is a column of 24 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsum aspect of the torso, separated by spinal discs....
.

Despite their name, there is some debate about whether they are strictly fish

Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
(as there is for lamprey

Lamprey

A lamprey is a parasitic marine animal with a toothed, funnel-like sucking mouth. While lampreys are well known for those species which bore into the flesh of other fish to hematophagy, these species make up the minority....
s), since they belong to a much more primitive lineage than any other group that is placed in the category of fish

Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
(Chondrichthyes

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired Fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone....
and Osteichthyes

Osteichthyes

Osteichthyes , also called bony fish, are a taxonomy group of fish that includes the ray-finned fish and lobe finned fish . The split between these two classes occurred around 440 mya ....
).

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Encyclopedia

Hagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade

Clade

Phylum

Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
but not a vertebral column

Vertebral column

Fish

Lamprey

Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
(Chondrichthyes

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired Fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone....
and Osteichthyes

Osteichthyes

Osteichthyes , also called bony fish, are a taxonomy group of fish that includes the ray-finned fish and lobe finned fish . The split between these two classes occurred around 440 mya ....
). 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. Although hagfish are sometimes called "slime eels," they are not eel

Eel

True eels are an order of fish, which consists of four suborders, 19 Family s, 110 genera and approximately 600 species. Most eels are predators....
s at all.

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, they have four hearts and two brains,and paddle

Paddle

A paddle is a tool used for pushing against liquids, either as a form of Marine propulsion in a boat or as an implement for mixing....
-like tail

Tail

The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals and birds....
s. They have cartilaginous

Cartilage

Cartilage is a type of dense connective tissue. It is composed of specialized cells called chondrocyte that produce a large amount of extracellular matrix composed of collagen fibers, abundant ground substance rich in proteoglycan, and elastin fibers....
skull

Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
s and tooth

Tooth

Teeth are small whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense....
-like structures composed of keratin

Keratin

Keratins are a family of fibrous protein; tough and insoluble, they form the hard but mineral structures found in reptiles, birds, amphibians and mammals....
. Colours depend on the species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
, ranging from pink

Pink

Pink is a pale red color; the use of the word for the color was first recorded in the late 17th century, describing the flowers of Dianthus, flowering plants in the genus Dianthus. Pink itself is a combination of red and white....
to blue

Blue

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440?490 Nanometre....
-grey

Grey

Grey or gray describes the tints and shades ranging from black to white. These, including white and black, are known as achromatic colors or neutral colors....
, and black

Black

Black is the color of objects that do not emit or reflection light in any part of the visible spectrum; they absorb all such frequencies of light....
or white

White

White is a color, the Color vision#Physiology of color perception which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in near equal amount and with high brightness compared to the surroundings....
spots may be present. Eye

Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
s are simple eyespots, not compound eyes that can resolve images. Hagfish have no true fin

Fin

A fin is a surface used to produce lift and thrust or to steer while traveling in water, air, or other fluid media. The first use of the word was for Fish anatomy#Fins of fish, but has been extended to include other animal limbs and man-made devices....
s and have six or eight barbels around the mouth and a single nostril

Nostril

A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation....
. Instead of vertically articulating jaw

Jaw

The jaw is either of the two opposable structures forming, or near the entrance to the mouth.The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals....
s like Gnathostomata

Gnathostomata

Gnathostomata is the group of vertebrates with jaws.The group is traditionally a superclass , broken into two top level groupings; cartilaginous fish, and all other members, including the familiar classes of bony fish, birds, mammals, reptiles, and amphibians....
(vertebrate

Vertebrate

Vertebrates are members of the subphylum Vertebrata, chordates with Vertebras or Vertebral columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae....
s with jaws), they have a pair of horizontal

Horizontal

Horizontal may refer*Horizontal plane, in astronomy, geography, geometry and other sciences and contexts*Horizontal coordinate system, in astronomy...
ly moving structures with tooth-like projections for pulling off food.

Circulatory system

The circulatory system

Circulatory system

The circulatory system is an organ that moves nutrients, gases, and wastes to and from cells to help fight diseases and help stabilize body temperature and pH to maintain homeostasis....
s of the hagfish have both closed and open blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the artery, which carry the blood away from the heart, the capillary, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from...
s, with a heart

Heart

The heart is a muscle organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods....
system that is more primitive than that of vertebra

Vertebra

A vertebra is an individual bone in the flexible column that defines vertebrate animals. The vertebral column encases and protects the spinal cord, which runs from the base of the cranium down the dorsal side of the animal until reaching the pelvis....
tes, bearing some resemblance to that of some worm

Worm

A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms....
s. This system comprises a "brachial heart

Heart

The heart is a muscle organ in all vertebrates responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in annelids, mollusks, and arthropods....
", which functions as the main pump, and three types of accessory hearts: the four hearts which carry blood

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
from intestines to liver

Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
, the "cardinal" heart(s) which move blood from the head to the body, and the "caudal" heart(s) which pump blood from the trunk and kidney

Kidney

The kidneys are Organ that have numerous biological roles. Their primary role is to maintain the homeostasis balance of bodily fluids by filtering and secreting Metabolomics#Metabolitess and minerals from the blood and excreting them, along with water , as urine....
s to the body. None of these hearts are innervated, so their function is probably modulated, if at all, by hormones.

Slime (and behavior)

Hagfish are long and vermiform

Worm

Slime

Slime may refer to:* Slime , a regular feature of several of Nickelodeon's television shows.* Gunge, a British colloquial name for a runny substance similar to paint, that is often featured in game shows....
or mucus

Mucus

In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect Epithelium in the respiratory,...
(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

Overhand knot

The overhand knot is one of the most fundamental knots and forms the basis of many others including the Noose, overhand loop, angler's loop, fisherman's knot and water 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 human 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. 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.

Free-swimming hagfish also "slime" when agitated and will later clear the mucus off by way of the same traveling-knot behavior. 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.

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

University of Queensland

The University of Queensland is one of Australia's premier learning and research institutions. The University is a founding member of the national Group of Eight, an alliance of research-strong, mostly "Sandstone universities" committed to ensuring that Australia has higher education institutions which are genuinely world class....
claiming the hagfish's eye as being significant to the evolution of more complex eyes

Evolution of the eye

The evolution of the eye has been a subject of significant study, as a distinctive example of a homology organ present in a wide variety of taxa....
. Hagfish eyespots when present can detect light, but as far as is known none can resolve detailed images.

Reproduction

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, with both ovaries and testes, but with female gonad

Gonad

The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells....
s which remain non-functional until the individual has reached a particular age, or possibly until it encounters particular environmental stresses. 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

Velcro

Velcro is a brand name of fabric hook-and-loop fasteners. It consists of two layers: a "hook" side, which is a piece of fabric covered with tiny hooks, and a "loop" side, which is covered with even smaller and "hairier" loops....
-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 larva

Larva

A larva is a young form of animal with indirect developmental biology, going through or undergoing metamorphosis .The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly....
l stage, in contrast to lamprey

Lamprey

Feeding

While polychaete

Polychaete

The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin....
marine worm

Marine worm

Any worm that lives in a ocean environment is considered a marine worm. Marine worms are found in several different phylum , including the Platyhelminthes, Nematoda, Annelida, Chaetognatha, Hemichordata, etc....
s 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 them.

Like leech

Leech

Leeches are annelids comprising the subclass Hirudinea. There are fresh water, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum....
es, they have a sluggish metabolism and can survive months between feedings. 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 dozens 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.

Classification

Eptatretus Cirrhatus (new Zealand Hagfish)

There has been long discussion in scientific literature about the hagfish being non-vertebrate

Invertebrate

An invertebrate is an animal lacking a vertebral column. The group includes 98% of all animal species ? all animals except those in the Chordate subphylum vertebrate ....
. Given their classification as Agnatha

Agnatha

Agnatha is a class or superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Many recent textbooks regard the group as paraphyletic but recent molecular data, both from rRNA and from mtDNA strongly supports living agnathans as monophyletic....
, Hagfish are seen as an elementary vertebrate in between Prevertebrate and Gnathostome. Recent molecular biology

Molecular biology

Molecular biology is the study of biology at a molecule level. The field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry....
analyses tend to classify hagfish as invertebrates (see references) within subphylum Craniata, because of their short molecular evolutive distance from Vertebrata (sensu stricto). A single fossil of hagfish shows that there has been little evolutionary change in the last 300 million years.

Genetic analysis

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

Chordate

Chordates are a group of animals that includes the vertebrates, together with several closely related invertebrates. They are united by having, at some time in their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail....
s.

Species

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. Some of the species are listed here:

Genus Eptatretus
Eptatretus

Eptatretus is a genus of hagfish....

Inshore hagfish, Eptatretus burgeri (Girard, 1855)
New Zealand hagfish
New Zealand hagfish

The New Zealand hagfish, Eptatretus cirrhatus, is a hagfish of the genus Eptatretus, found in south and east Australia, and around New Zealand, at depths of between 40 and 700 metres....
, Eptatretus cirrhatus (Forster, 1801)
Black hagfish, Eptatretus deani (Evermann & Goldsborough, 1907)
Guadalupe hagfish, Eptatretus fritzi Wisner & McMillan, 1990
Eptatretus goliath Mincarone & Stewart, 2006
Sixgill hagfish, Eptatretus hexatrema (Müller, 1836)
Eptatretus lopheliae Fernholm & Quattrini, 2008
Shorthead hagfish, Eptatretus mcconnaugheyi Wisner & McMillan, 1990
Eptatretus mendozai Hensley, 1985
Eightgill hagfish, Eptatretus octatrema (Barnard, 1923)
Fourteen-gill hagfish, Eptatretus polytrema (Girard, 1855)
Fivegill hagfish, Eptatretus profundus (Barnard, 1923)
Cortez hagfish, Eptatretus sinus Wisner & McMillan, 1990
Gulf hagfish
Gulf hagfish

The gulf hagfish is currently the only known species with the ability to enter brine pools, or pools of extremely high salt content, unharmed. These pools resemble lakes on the ocean floor....
, Eptatretus springeri (Bigelow & Schroeder, 1952)
Pacific hagfish
Pacific hagfish

The Pacific hagfish is a species of hagfish. It lives in the mesopelagic to abyssal Pacific ocean, near the ocean floor. It is a Agnatha, a throwback to the Paleozoic Era when fish evolved....
, Eptatretus stoutii (Lockington, 1878)
Eptatretus strickrotti
Eptatretus strickrotti

Eptatretus strickrotti is a hagfish of the genus Eptatretus, found in the Pacific Ocean depths south of Easter Island. The hagfish was found in March 2005 by DSV Alvin pilot Bruce Strickrott, and a year later was determined by scientists to be a new species....
Møller & Jones, 2007

Genus Myxine

Patagonian hagfish Myxine affinis Günther, 1870
Myxine australis Jenyns, 1842
Cape hagfish, Myxine capensis
Whiteface hagfish, Myxine circifrons Garman, 1899
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
Hagfish (or Atlantic hagfish), Myxine glutinosa
Myxine hubbsi Wisner & McMillan, 1995
Myxine hubbsoides Wisner & McMillan, 1995
White-headed hagfish, Myxine ios
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

Genus Nemamyxine

Nemamyxine elongata Richardson, 1958
Nemamyxine kreffti McMillan and Wisner, 1982

Genus Neomyxine

Neomyxine biniplicata (Richardson and Jowett, 1951)

Genus Notomyxine

Notomyxine tridentiger (Garman, 1899)

Genus Paramyxine

Paramyxine atami Dean, 1904
Paramyxine cheni Shen and Tao, 1975
Paramyxine fernholmi Kuo, Huang and Mok, 1994
Paramyxine sheni Kuo, Huang and Mok, 1994
Paramyxine wisneri Kuo, Huang and Mok, 1994

Genus 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)

Hagfish

Physical characteristics

Body features

Circulatory system

Slime (and behavior)

Eye

Reproduction

Feeding

Classification

Genetic analysis

Species

External links