Agnatha is a class or subphylum of fish in the chordate phylum distinguished from the Gnathostomata by their lack of jaws. Among the Agnatha are two living groups, the lampreys and the hagfish, and a number of fossil forms that were common during the Ordovician, Silurian, and Devonian periods, 500–350 million years ago.


The modern lampreys are eel-like and feed on fish by attaching themselves to their prey and sucking their body fluids. Hagfish live by feeding on dead or dying fish and are, unlike the lampreys, exclusively marine.