Ancient Species

Agnaths
(Jawless Fish)

Agnaths are fishlike creatures characterized by a slit-like mouth and no jaw. Most had a bony shield on the head and a flexible coat of plates. 

Agnaths first appeared in the Silurian Period (434 to 408 million years ago). They were largely replaced by ray-finned fish from  the Devonian Period (408 to 354 million years ago) onward. There are only two types of these jawless fish today: hagfish and lampreys.