Arandaspis, a genus of jawless fish, is one of the oldest known vertebrates. It probably obtained its food by filtering the water.
The streamlined body was covered with rows of knobbly scales of thick bone. The front of the body and the head were also protected by armoured plates, with openings for the eyes, nostrils and gills.
Arandaspis had no fins and used its flattened tail for propulsion. We can therefore assume that it swam like a tadpole.