Myxine glutinosa, also known as the Atlantic hagfish, is a type of jawless fish belonging to the class Myxini.
Description The Atlantic hagfish may grow up to .75 metres (2+1⁄2 ft) long, with no eyes and no jaws; its star-shaped mouth is surrounded by 6 mouth barbels. Their eyes also lack a lens and pigment (features found in the eyes of all other living vertebrates). There is a single gill slit on each side of the eel-like body. It has a total of 88–102 pores from which it can exude a slimy mucus. Hagfish have very flexible bodies which allow them to manipulate themselves into knots. The knots created by the hagfish remove mucus from the body, allow them to escape tight spaces, and pull potential prey from burrows, and because they have no opposable jaws it helps create leverage while they eat.
Similar species A related species, the Gulf hagfish (Eptatretus springeri), occurs in the Gulf of Mexico. To distinguish these two types of hagfishes, we can look at their lateral line and eyes, the Myxine glutinosa has no lateral line system and also an unpigmented, cornea-like window in the skin overlying the eye.
Distribution The distribution of Myxine glutinosa in the eastern Atlantic Ocean extends from the western Mediterranean Sea and Portugal to the North Sea, Skagerrak, Kattegat and the Varanger Fjord. It is also found in the western Atlantic Ocean from Baffin Island, Canada south to North Carolina. They live on muddy ocean floors at depth ranges of about 20 to 1000 meters.
Biology Like most fish that live on the bottom of the ocean, the Atlantic Hagfish's body color on the dorsal side varies depending on the color of the bottom of the ocean. The most common colors are brown, reddish or purplish, brown, or grey; for the ventral side, the color will be paler. There are differences in the lateral line system among different types of hagfish as well. Instead of having a simple form of a lateral system like the hagfish Eptatretus, an adult Myxine glutinosa has no lateral line system. The Atlantic Hagfish has many unique features. Plenty of discussions on the evolutionary morphology of the Myxine glutinosa eyes occur, with some scientists trying to compare it with the retina of lampreys. The Atlantic Hagfish possesses a more ancestral vertebrate eye form, and the lamprey possesses a more derived form. Other scientists have suggested that the Atlantic Hagfish may have possessed more complex eyes that regressed due to environmental factors like little to no light or the need for burrowing. Besides the fact that the eyes of Myxine glutinosa lack both a lens and a vitreous body, experimental studies carried out by Newth and Ross (1955) also suggested that the eye of Myxine glutinosa lacks a photoreceptive function. Kaj Holmberg has described how each hagfish species has differentiated external appearances, and Myxine glutinosa has an unpigmented, cornea-like window in the skin overlying the eye. Finally, some previous works on Myxine glutinosa have led to the conclusion that the retina in these animals is functionless, but the electro-physiological experiments by Kobayashi (1964) showed the eye of Myxine garment (a closely related species) can respond to light stimulation, which may suggest that Myxine glutinosa could respond to light stimulation. The respiratory anatomy of Myxine glutinosa is similar to other hagfish, with a single, median nostril at the tip of the snout surrounded by two pairs of barbels. During the respiratory process, water will flow into this median nasal to the pharynx and reach every gill pouch.
Mucus The Atlantic Hagfish are known for their ability to produce slime: a thick, transparent gel that is cohesive and substantial. Myxine glutinosa can secrete 2 types of slime: the epidermal mucus and the extruded slime. Epidermal mucus helps the prevention of pathogens and is produced all the time while extruded slime is only observed during feeding, provocation, or stress. This slime is not produced by the hagfish directly. The glands inside the hagfish's body excrete "pre-slime", which are protein molecules that can expand in volume when reacting with water. In producing the slimes. "threads" that are produced by the thread cells in their gland that will unravel when they touch the seawater. When those 2 substances mix at the same time with the seawater, the slime appears in just a fraction of a second. Different species of hagfish also have different slime compositions as well as slime refilling times. It is believed that it usually takes about 3 to 4 weeks for the slime glands to fully refill. This slime is vital to the survival of the Atlantic hagfish as it can distract and affect predators' respiratory systems, reducing the force of squeezing into big food. When the hagfish no longer need the slime, they will form the "body knot" to scrape off all the slime on the body from the head to the tail. More recent research has revealed the active hunting activities that this species of hagfish has. Furthermore, although this type of hagfish seems to be primitive, its simple body displays a great amount of dexterity. This is also related to how they can form the body knot- as the previous part indicates, the knot can be forcefully propagated in both directions to escape from predators or gain leverage for tearing apart large chunks of food. This leads to the continuous study of hagfish locomotion and keeps improving our understanding of the collective diversity in elongated animals. There are additional differences in the lateral line system among different types of hagfish. Instead of having a simple form of a lateral system like the hagfish Eptatretus, an adult Myxine glutinosa has no lateral line system. Scientists often compare Hagfish and lampreys since both are referred to as jawless fish (agnathans). They are the only survivors from the Agnathan stage during the vertebrate evolution. Gnathostomes (jawed vertebrates) also share a common ancestor with those hagfish.
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