Only the front third of an individual arthrodire was heavily armored. Sometimes the rest of the body was covered with very tiny scales, which were probably not bony since they fossilize leaving only a faint stain. Only some of the antiarchi species found on Orkney have scales that preserve well.
It is not possible to generalize about placoderm feeding mechanisms because they differ from species to species. However, most of the placoderms found on Orkney have well developed jaws often with tiny teeth like structures. They may have fed on tiny fish or invertebrates. It is also suggested that they were ambush predators swallowing their prey whole.