Pteraspis

Pteraspis (from πτερόν pteron 'wing' or 'fin' and ἀσπίς aspís 'shield') is an extinct genus of pteraspidid heterostracan jawless fish. It lived from the Lochkovian to Eifelian epochs of the Devonian period in what is now Brazil (Eifelian Maecuru Formation), Britain (Lochkovian Ditton Group), Ukraine (Lochkovian Ivane Suite, Pragian Babin Sandstone) 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 due 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, which is good for swimming. 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. Some records are found in association with marine fossils, while some others are found in freshwater environment.

Pteraspis grew to an estimated length of 20 cm.