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Morphological and paleoecological analysis of the Ordovician ankyroid Lagynocystis (Stylophora: Echinodermata)

Published online by Cambridge University Press:  20 May 2016

Ronald L. Parsley
Ronald L. Parsley*
Affiliation:
Department of Geology, Tulane University, New Orleans, Louisiana 70118,
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Abstract

Despite its atypical thecal plate pattern, Lagynocystis pyramidalis (Jaekel, 1918) (Middle Ordovician, Northern Gondwanaland) is composed of normally positioned marginal plates on the left side of the theca, whereas those on the right side are shortened or missing in comparison with marginal plates of other ankyroids. The only somatic on the lower thecal surface is the CS plate. The abnormally long distal aulacophore, reduced theca, and internal ctenoid organ are interpreted as adaptations to deep water, dysaerobic environmental conditions. Ctenoid organ morphology is re-evaluated and is interpreted to have both feeding and respiratory functions. Loss of plates relative to a presumed ancestor similar to Barrandeocarpus has resulted in torsion that places somatic platelets, originally on the superior face, onto the inferior face and in contact with both CS and M′3 plates.

Type
Research Article
Information
Journal of Paleontology , Volume 74 , Issue 2 , March 2000 , pp. 254 - 262
Copyright
Copyright © The Paleontological Society 2000

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