|GRAPTOLITE FINE STRUCTURE|
|Cortical bandages in Orthograptus gracilis (Roemer)
|Graptolite Net | Graptolites & Graptoliters | Evolution of Graptolites | Cephalodiscoidea | Rhabdopleuroidea|
|A cortical bandage is the fundamental unit of cortex in graptolites and its structure is probably universal.
For the first time the cortical bandages were found on thecal walls of Orthograptus gracilis by P. KRAFT (1926), who called them Chitinverdikungsbänder. Similar structures were described also by A. EISENACK (1959) on the sicula of this graptolite.
D. ANDRES (1976, 1977) discovered with the light microscope that the periderm surface in O. gracilis is densely covered with ribbon-like structures, who called them Cortex-Bänder or Verdickungsbänder. According to him, the entire cortical layer consists of such ribbons, which were deposited by the cephalic discs of zooids creeping over the surface of the rhabdosome. Independently, almost at the same time, P.R. CROWTHER and B. RICKARDS (1977) drew similar conclusions from scanning electron microscopy studies.
To the right is D. Andres' (1976) drawing showing cortical bandages in Orthograptus gracilis.
Piotr Mierzejewski, The Count of Calmont & Countess Maja Anna Korwin-Kossakowska
|To the left is a scanning electron micrograph of densely packed cortical bandages in O. gracilis from an Ordovician glacial boulder of Baltic origin (by P. Mierzejewski).
Andres, D. 1976. Graptolithen aus Ordovizischen Gechieben und die frühe Stammesgeschichte der Graptolithen. - Inaugural-Dissertation zur Erlangung der Doktorwürde des Fachbereiches 24 (Geowissenschaften) der Freien Universität Barlin. Berlin, 77pp. [The same text was published in Paläontologische Zeitschrift in 1977].
Crowther, P. R. & Rickards, R.B. 1977. Cortical bandages and the graptolite zooid. - Geologica et Palaeontologica 11, 9 - 46.
Crowther, P.R. 1981. The fines structure of graptolite periderm. - Special Papers in Palaeontology 26, 1- 119.