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.