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agnathan
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lamprey Illustration of a Petromyzon, a jawless fish with an elongated, eel-like body and a rounded mouth, shown with a scale bar indicating 10 centimeters and 4 inches for size reference. Vertebrate species counts Illustration of a Myxine, or hagfish, showing its long, slender, eel-like body with smooth skin. A scale bar below indicates length in centimeters and inches for size reference. A branching diagram shows the evolutionary relationships among fossil and modern jawless fishes (Agnatha), with illustrations of Petromyzon, Myxine, Pharyngolepis, Pteraspis, Hemicyclaspis, and Drepanaspis along a timeline from the Ordovician period to the present. phyletic family tree for fishes
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lamprey
lamprey Lamprey (Lampetra) on rainbow trout.

agnathan

vertebrate
Also known as: Agnatha, jawless fish
Written by
Peter L. Forey
Research associate, The Natural History Museum, London.
Peter L. ForeyAll
Fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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History

agnathan, (superclass Agnatha), any of approximately 160 living species that make up the group of primitive jawless fishes that includes the lampreys (order Petromyzoniformes) and hagfishes (order Myxiniformes), as well as several extinct groups. Hagfishes are minor pests of commercial food fisheries of the North Atlantic, but lampreys, because of their parasitic habit, have been a serious pest of food fisheries in the Great Lakes in North America, where they have reduced the numbers of...

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