What do agnathans eat

Treatment of Agnatha. CME Programs on Agnatha. Agnatha en Espanol. Agnatha en Francais. Agnatha in the Marketplace. Patents on Agnatha. List of terms related to Agnatha. 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. There is no parental care in the Agnatha class. The Agnatha are ectothermic , with a cartilaginous skeleton , and the heart contains 2 chambers. Although they are superficially similar, many of these similarities are probably shared basal characteristics of ancient vertebrates, and modern classifications tend to place hagfish into a separate group the Myxini or Hyperotreti , with the lampreys Hyperoartii being more closely related to the jawed fishes.

Agnathans are characterized by seven or more pairs of gill pouches. 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. These features are also shared with the gnathostomes —vertebrates with jawed mouths and paired appendages see below.

Lampreys also have a dorsal tubular nerve cord with a well-differentiated brain, a small cerebellum, and 10 pairs of nerves.

The classification of lampreys is still debated, but they clearly represent one of the oldest divergences of the vertebrate lineage.

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. According to common hagfish mythology, they can fill a 5-gallon bucket with the stuff in mere minutes.

This slime gives hagfish a slippery exit when attacked by predators. A larger fish looking for a meal instead gets a mouth full of slime, while the hagfish can slide away.

Although their eating habits seem disgusting, hagfish help clean and recycle dead animals from the seafloor. They also serve as a food source for fish, seabirds and seals—at least those that can make it through the slime. Aganthans do not have hinged upper and lower jaws, instead they have unhinged circular mouths. They also do not have paired appendages like other vertebrates but have a tail and a caudal fin. The internal skeleton is made from cartilage and their body covering is skin.

They also do not have a proper stomach, but have a long gut which is the same for its entire length. Lampreys on sale in a trading floor of a fish supermarket. Many lampreys are parasites that use their toothed, funnel-like and sucker-like mouths to attach to a fish or mammal host. They use the many teeth in their mouths and on their tongues to shred the flesh of their host. Lampreys grow to a length of 13 to centimetres.