The structure of the exoskeleton of the Tremataspidoidei and its significance in the taxonomy of Osteostracans (Agnatha)

In contrast to other groups of Osteostracans, Tremataspis-like forms (Tremataspidoidei) are characterized by a considerable polymorphism in the structure of the exoskeleton. An attempt is made to distinguish the exoskeletal characters for the taxa of different ranks, based on a detailed analysis of the microstructure of the external skeleton in the species belonging to this group. It was observed that the characters of the exoskeleton could be used only in combination with characters connected with internal structure of Osteostracans.