Tremataspis schmidti
Anaspid
Upper Silurian
Rootsikula Formation
Island of Oesel, Estonia

28mm on 66mm matrix

Tremataspis is a genus of armored jawless fish of the Subclass Osteostraci.  This group bore one body shield with holes for the mouth, eyes and other sensory organs.

The osteostracans appeared during the Early Silurian and were quite diverse by the Early Devonian but they became rare and died out by the end of the period.