|Acta Palaeontologica Polonica 2000, 45, 1, 71-84
|[Text] Abstract - Light microscopic, SEM and TEM investigations show that the periderm of the
problematic Ordovician microfossil Xenotheka klinostoma Eisenack, 1937 is built of five layers: inner
lining, endocortex, fusellum, ectocortex and outer lining. The outer lining is made of previously
unknown material named here verrucose fabric. The outer lining was presumably an adaptation
which aided survival through periods of unfavourable conditions. The general morphology of the
test as well as of the fusellar structure of the wall indicate that Xenotheka is an aberrant camaroid
graptolite. This finding thus extend the upper stratigraphic limit of the Order Camaroidea from the
Early Arenig to Llandeilo.
Xenotheka klinostoma Eisenack, 1937.
TEM micrograph - Transverse section
through the autothecal periderm.
Abreviations: e, ectocortex; en,
i, inner lining; l, electron dense line;
o, outer lining; v, verruca;
ve, verruca vesicle; vf, interfibrillar
Xenotheka klinostoma is a distinctive sessile
organic microfossil known from the Lower
Ordovician beds of the Isle of Ă–land
(Sweden) and from Ordovician glacial
boulders. The species also occurs in the
Ordovician of Estonia. J. Jansonius (1964)
considered it to be a chitinozoan incertae
sedis. Some authors interpreted Xenotheka
as a member of Foraminifera.