Agnatha


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Agnatha

[′ag·nə′thə]
(vertebrate zoology)
The most primitive class of vertebrates, characterized by the lack of true jaws.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Thelodontier-, Akanthodier- und Elasmo-branchier-Schuppen aus dem Unter-Devon der Kanadischen Arktis (Agnatha, Pisces).
A new ctenaspid (Agnatha, Heterostraci) from the Early Devonian of Nevada, with comments on taxonomy, paleobiology and paleobio-geography.
A new species of Ariaspis (Agnatha: Heterostraci) from the Late Silurian of the Canadian Arctic.
Acrosome reaction in spermatozoa of the hagfish Eptatretus burgeri (Agnatha).
Acrosome reaction in spermatozoa from hagfish (Agnatha) Eptatretus burgeri and Eptatretus stouti: acrosomal exocytosis and identification of filamentous actin.
Novye dannye po Karelosteus weberi Obruchev (Agnatha: Heterostraci) [New data on Karelosteus weberi Obruchev (Agnatha: Heterostraci)].
Uus psammosteiid (Agnatha, Heterostraci) Amata regionaalsest lademest Peadevonivaljalt ja diskreetsete mikromeersete elementide tuubid sugukonnas Psammosteidae
Thelodonts (Agnatha) from the basal beds of the Kuressaare Stage, Ludlow, Upper Silurian of Estonia.
Thelodonts (Agnatha) from the Lower Silurian (Wenlock) deposits of the northwest of Belarus.
This error was corrected by Traquair (1896), who named the genus Turinia to contain Powrie's species and grouped it with other well-preserved Scottish thelodonts as jawless vertebrates (Agnatha).