Pteraspis was a Devonian heterostracan with a beak-like rostrum in front of its head and wing-like things sticking out of the two back sides of its head armor. Pteraspis means "wing shield."
It had a protective spine pointing backwards that would probably harm a predator that would try to eat it. Pteraspis was only about 8" and there were monster predators around like Eusthenopteron and Dunkleosteous. Pteraspis was jawless, so it had to suck in plankton through its mouth.
Pteraspis was one of the last heterostracans and one of the last placoderms because placoderms went extinct at the end of the Devonian and so did the heterostracans (because heterostracans were placoderms).