They are in the class Agnatha , designated for fish without jaws around species in total. Although they are jawless , hagfish have two rows of tooth-like structures made of keratin that they use to burrow deep into carcasses.
They can also bite off chunks of food. While eating carrion or live prey, they tie their tails into knots to generate torque and increase the force of their bites. One hagfish species is critically endangered, two are endangered, six are vulnerable to extinction and two are near-threatened. No one is sure whether hagfish belong to their own group of animals, filling the gap between invertebrates and vertebrates, or if they are more closely related to vertebrates. The only known fossil hagfish , from million years ago, looks very much like a modern hagfish, leading some scientists to speculate that it has changed little since then.
To ward off predators and other fish trying to steal their meals, hagfish produce slime. When harassed, glands lining their bodies secrete stringy proteins that, upon contact with seawater, expand into the transparent, sticky substance. The class Myxini includes at least 70 species of hagfishes—eel-like scavengers that live on the ocean floor and feed on living or dead invertebrates, fishes, and marine mammals Figure 1.
Although they are almost completely blind, sensory barbels around the mouth help them locate food by smell and touch. They feed using keratinized teeth on a movable cartilaginous plate in the mouth, which rasp pieces of flesh from their prey. These feeding structures allow the gills to be used exclusively for respiration, not for filter feeding as in the urochordates and cephalochordates.
Hagfishes are entirely marine and are found in oceans around the world, except for the polar regions. Unique slime glands beneath the skin release a milky mucus through surface pores that upon contact with water becomes incredibly slippery, making the animal almost impossible to hold.
This slippery mucus thus allows the hagfish to escape from the grip of predators. Hagfish can also twist their bodies into a knot, which provides additional leverage to feed.
Sometimes hagfish enter the bodies of dead animals and eat carcasses from the inside out! Interestingly, they do not have a stomach! Hagfishes have a cartilaginous skull, as well as a fibrous and cartilaginous skeleton, but the major supportive structure is the notochord that runs the length of the body. In hagfishes, the notochord is not replaced by the vertebral column, as it is in true vertebrates, and thus they may morphologically represent a sister group to the true vertebrates, making them the most basal clade among the skull-bearing chordates.
Figure 2. The class Petromyzontida includes approximately 40 species of lampreys, which are superficially similar to hagfishes in size and shape. However, lampreys possess extrinsic eye muscles, at least two semicircular canals, and a true cerebellum, as well as simple vertebral elements, called arcualia —cartilaginous structures arranged above the notochord. Be alerted to news on Agnatha. News trends on Agnatha. Blogs on Agnatha.
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Agnatha Greek , "no jaws" is a paraphyletic [1] superclass of jawless fish in the phylum Chordata , subphylum Vertebrata. It has existed since the Cambrian , and continues to live now. There are two extant groups of jawless fish sometimes called cyclostomes , the lampreys and the hagfish , with about species in total. Although they are in the subphylum Vertebrata, hagfish technically do not have vertebrae; they are sometimes classified in Craniata.
In addition to the absence of jaws, Agnatha are characterised by absence of paired fins ; the presence of a notochord both in larvae and adults; and seven or more paired gill pouches. There is a light sensitive pineal eye homologous to the pineal gland in mammals. All living and most extinct Agnatha do not have an identifiable stomach or any appendages. Fertilization and development are both external.
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