Microstructure of the shell of the brachiopod Wyndhamia clarkei

Abstract

In the shell of Wyndhamia clarkei (Etheridge) taleolar calcite is texturally similar to the calcite comprising the layers deposited by the epithelium forming the areas of attachment of the muscles. The remainder of the shell is composed of sheets of blades arranged like the components making up the crossed‐bladed shells of Terrakea solida (Etheridge & Dun) and Streptorhynchus pelicanensis Fletcher. The crystallographic z‐axes of the calcite crystals comprising the blades of the shell of Wyndhamia clarkei are disposed approximately normal to the surface of the shell, like the z‐axes of the calcite crystals in the primary and secondary layers of shells of the terebratulid Marinurnula mantuanensis Campbell. The nature of taleolae is discussed and it is speculated that a functional relationship may have existed between the type of epithelium which formed taleolae and the growth mechanism envisaged for the crossed‐bladed microstructural fabric.