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DESMOGRAPTUS MICRONEMATODES, A SILURIAN DENDROID GRAPTOLITE, AND ITS ULTRASTRUCTURE |
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| Authors: | by KATE M SAUNDERS DENIS E B BATES† JOANNE KLUESSENDORF‡ DAVID K LOYDELL DONALD G MIKULIC§ |
| Institution: | School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth PO1 3QL, UK;email:; Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK;e-mail:; Weis Earth Science Museum, University of Wisconsin-Fox Valley,1478 Midway Road, Menasha, Wisconsin 54952, USA;email:; Illinois State Geological Survey, 615 East Peabody Drive, Champaign, Illinois 61820, USA;email: |
| Abstract: | Abstract: Desmograptus micronematodes from Thornton quarry, Cook County, Illinois, USA, remarkably preserved in relief and encased in pyrite, is described. The internal details of the thecae, and of the stolon system, examined using the SEM, allow the reconstruction of the growth of a stipe. The stolons and stolonal nodes are formed of a dense crassal fabric, and are surrounded by a loose fabric of three-dimensional fibrils. The nodes have a complex structure of three boxes with proximal and distal nozzles. The base of a bitheca, and the base of each autothecal cup, has a central nozzle surrounded by a unique honeycomb fabric. The ultrastructure of the cortical fibrils, with their clockwise striations, is similar to that in Dendrograptus , and may be universal in the graptolites. The nodes of the stolon system appear identical to those of Acanthograptus and other dendroids, but differ from those of the extant hemichordate Rhabdopleura , which have only a diaphragm, and lack box structures. |
| Keywords: | autotheca bitheca Desmograptus dendroid graptolite stolon ultrastructure |