Graptolite nature of the Ordovician microfossil Xenotheka

Light microscopic, SEM and TEM investigations show that the periderm of the problematic Ordovician organic microfossil Xenotheka klinostoma Eisenack, 1937 is built of Eve layers: inner Lining, endocortex, fusellum, ectocortex and outer lining. The outer lining is made of a previously unknown materia l named here verrucose fabric. The outer lining was presumably an adaptatio n which aided survival through periods of unfavourable conditions. The gene ral morphology of the test as well as of the fusellar structure of the wall indicate that Xenotheka is an aberrant camaroid graptolite. This finding t hus extends the upper stratigraphic limit of the order Camaroidea from the early Arenig to Llandeilo.