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Agnatha

Agnatha is a superclass of jawless fish. They appear in the fossil record during the Cambrian, about 450 million years ago.

The name “Agnatha” is derived from the Greek words “a,” meaning “without,” and “gnathos,” meaning “jaw.” These ancient fish lack true jaws, which distinguish them from more advanced fish groups like cartilaginous and bony fish. Agnatha is a diverse group that includes hagfish and lampreys, both of which have unique characteristics and evolutionary significance.

Hagfish (Myxini): Hagfish are primitive, eel-like creatures that belong to the superclass Agnatha. They are known for their slimy appearance and behavior. Some key features of hagfish include:

  1. Lack of Jaws: Hagfish are jawless fish, and they use a specialized rasping tongue to feed on decaying organisms and other organic matter.
  2. Slime Production: Hagfish are famous for their ability to produce copious amounts of slime as a defense mechanism. This slime helps them escape from predators by making them difficult to grasp.
  3. Lack of Vertebrae: Hagfish have a cartilaginous structure, and they lack true vertebral columns. Instead, they possess a notochord, which is a flexible rod that provides support.

Lampreys (Petromyzontida): Lampreys are another group of jawless fish within the superclass Agnatha. They are known for their parasitic and non-parasitic species. Some characteristics of lampreys include:

  1. Parasitic Feeding: Many lampreys are parasitic, attaching themselves to other fish using their circular, toothed mouths. They feed on the host’s blood and body fluids.
  2. Lifecycle: Lampreys often undergo a fascinating lifecycle, which involves a transition from a filter-feeding larval stage to a parasitic adult stage.
  3. Eel-Like Appearance: Lampreys have elongated, eel-like bodies. They lack paired fins but have a dorsal fin running along their back.

Evolutionary Significance: Agnatha, including hagfish and lampreys, are considered primitive vertebrates that provide insight into the early stages of vertebrate evolution. Their lack of jaws and other features set them apart from more advanced vertebrates. Studying Agnatha helps scientists understand the evolutionary steps that led to the development of jaws and other complex adaptations in later fish groups.