Pteraspis

Pteraspis (meaning wing shield) is an extinct genus of primitive jawless fish that lived in the Devonian period of what is now Britain and Belgium.

Description
Like other heterostracan fishes, Pteraspis had a protective armored plating covering the front of its body. Though lacking fins other than its lobed tail, it is thought to have been a good swimmer thanks to stiff, wing-like protrusions derived from the armoured plates over its gills. This, along with the horn-like rostrum, made Pteraspis very streamlined in shape; a perfect quality for a good swimmer. Pteraspis also had some stiff spikes on its back, possibly an additional form of protection against predators. It is thought to have fed from shoals of plankton just under the ocean surface,[1] and is found in association with marine fossils.[2][3]

Pteraspis grew to a length of 8 inches (20 centimeters).