Ostracoderms, jawless fishes of Silurian and Devonian times. Shown in one sketch as they might have appeared while searching for food on the floor of a Devonian sea. All were probably suspension-feeders, but employed a strong pharyngeal pump to circulate water rather than the much more limited mode of ciliary feeding used by their protovertebrate ancestors and by amphioxus today. Modern lampreys are believed to be derived from the anaspid group.
EDIT: Did I mention they have armor? ‘Cause they were totally armored fish. HOW COOL.