Epithelial cell moulds preserved in the earliest acrotretid brachiopods from the Cambrian (Series 2) of the Three Gorges area, China

Abstract

Distinctive moulds of epithelial cells are known to occur on valve interiors in early Palaeozoic acrotretid brachiopods but morphological variation and distributional patterns of the epithelial cells imprints remains poorly known. Herein, we present for the first time a detailed study of exquisitely preserved epithelial cell moulds and shell micro-structures in acid-etched material of the earliest acrotretid brachiopod Eohadrotreta zhenbaensis from the Shuijingtuo Formation (Cambrian Series 2) of Aijiahe section, approximately 25 km north-west of Yichang City, western Hubei Province. The ventral and dorsal epithelial cell moulds (on average 18 μm across) are usually isometrically convex or concave polygonal with a variable outline (tetragon, pentagon and hexagon). Investigation of the new material demonstrates that the disposition of pronounced epithelial cell pustules or depressions in shell interiors most likely is associated with regions of thickened muscle attachments in ventral and dorsal valves – a character that potentially could be of use in taxonomy, though detailed comparative studies of such epithelial microstructures of acrotretids and other brachiopod taxa remain to be done.

Keywords:

• Epithelial cell moulds
• acrotretid brachiopods
• Early Cambrian
• Shuijingtuo Formation
• polygonal microstructures

Acknowledgements

Lars Holmer (Uppsala) is thanked for providing access to facilities and practical assistance when Zhiliang Zhang stayed in Sweden for a three-month visiting study at Uppsala University. Thanks are also extended to Profs. Bing Guo and Xiaohong Su in Northwest University (Xi’an) for their kind providing of epithelial sections of recent invertebrates for comparison, and Dr Timothy P. Topper (Stockholm) for practical advice, and to Miss Feiyang Chen and Mr Xiaoguang Yang (Xi’an) for valuable discussions, as well as to Mrs Juanping Zhai and Qingchun Feng for sample preparation in Xi'an. Thanks are also due to the editor Christian B. Skovsted and anonymous reviewers for their constructive and critical comments, which helped improve the manuscript.

Funding

This work has been supported by the National Natural Science Foundation of China (Grant 41425008) the National 973 program (2013CB835002) and 111 projects of China (P201102007) and the Postgraduate Creation Program of Northwest University (YZZ14025).