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Zooidal anatomy in Ordovician and Carboniferous trepostome bryozoans

Abstract

Fossil bryozoans sometimes contain fossilised brown bodies which remain after polypide degeneration. Position and shape of brown bodies as well as different skeletal diaphragms within living chambers allow outlining of autozooid anatomy in Palaeozoic trepostome bryozoans. In some trepostome bryozoans short autozooids were restricted by complete basal diaphragms to distal parts of autozooecia. In species with alternating hemiphragms, as in the specimen ofHemiphragma sp. described here, long autozooids occupied the entire autozooecial chambers. Their short polypides were positioned in distal parts of the autozooid. Both anatomic types correspond to the progressive polypide cycle afterBoardman. For species with ring septa, non-alternating hemiphragms (studied in an example ofNipponostenopora karatauensis) as well as without any diaphragms the stationary type of polypide cycle seems also to be possible. In that case, the polypides should be as long as the cystid.

Zusammenfassung

Fossile Bryozoen enthalten manchmal fossilisierte braune Körper, welche infolge der Degenration des Polypides entstehen. Position und Form der braunen Körper wie auch verschiedene Diaphragmen in Wohnkammern erlauben einige Schlüsse über Anatomie der Autozooide in Paläozoischen trepostomen Bryozoen. In einigen trepostomen Bryozoen waren kurze Autozooide mit kompletten basalen Diaphragmen auf distale Teile der Kolonien begrenzt. Taxa mit alternierenden Hemiphragmen wie das beschriebene Exemplar vonHemiphragma sp. besaßen lange Autozooide, welche die ganzen Wohnkammern ausfüllten. Ihre kurzen Polypide befanden sich in den distalen Teilen der Autozooide. Die beiden anatomischen Typen entsprechen dem progressiven Polypidenzyklus nachBoardman. Für Taxa mit ringförmigen Diaphragmen, nichtalternierenden Hemiphragmen (untersucht am Beispiel vonNipponostenopora karatauensis) wie auch ohne Diaphragmen scheint der stationäre Polypidenzyklus auch möglich. In diesem Fall sollen die Polypide genau so lang sein wie der Cystid.

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Ernst, A., Voigt, E. Zooidal anatomy in Ordovician and Carboniferous trepostome bryozoans. Paläontol Z 76, 339–345 (2002). https://doi.org/10.1007/BF02989869

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Keywords

  • Bryozoa
  • anatomy
  • Ordovician
  • Carboniferous

Schlüsselwörter

  • Bryozoa
  • Anatomie
  • Ordovizium
  • Karbon