Agnatha

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Related to jawless fish: coelacanth, cartilaginous fish

Agnatha

[′ag·nə′thə]
(vertebrate zoology)
The most primitive class of vertebrates, characterized by the lack of true jaws.

Agnatha

 

a superclass of lower vertebrate animals. Agnatha are distinguished from all the remaining vertebrates, the Gnathostomata, by the absence of real jaws, and, in the ones living today, by the absence of paired extremities, as well as by the presence of an unpaired nostril. Agnatha are also called Marsipobranchia, because their gills look like pouches. The branchiate skeleton is located outside the pouches and has the appearance of a complete lattice (and not broken gill arches, as in fish) or is fused with the external shell. Agnatha is the most ancient group of vertebrates, widely distributed in the Silurian and Devonian periods. Fossil Agnatha (Ostracodermi) had a well-developed external and partially ossified internal skeleton. Their remains are the leading fossils for the Silurian and Devonian periods.

Of contemporary fauna, only representatives of the class Cyclostomata—the lampreys and hagfish—remain of the Agnatha.

REFERENCES

Berg, L. S. Sistema ryb. Moscow-Leningrad, 1940.
Osnovy paleontologii: Bescheliustnye, ryby. Moscow, 1964.
References in periodicals archive ?
Writing about their study in the journal PLoS Biology, the researchers said that the first vertebrates to have teeth were a group of eel-like jawless fish, known as the conodonts, which had teeth not in their mouth, but lining the throat.
Instead, these early jawless fish appear to have had skulls and other skeletal structures made of cartilage, says Simon Conway Morris of the University of Cambridge in England, who collaborated with the Chinese team.
Washington, July 21 (ANI): In a new research, scientists have discovered that the sea lamprey, which emerged from jawless fish first appearing 500 million years ago, dramatically remodels its genome.
Scientists in 1976 identified the fossils, called Anatolepis, as the scales of a jawless fish.