Article: Variation in the cardinalia of the brachiopod Ptychopleurella bouchardi (Davidson) from the Wenlock Limestone of Wenlock Edge, Shropshire

In specimens of the orthacean brachiopod Ptychopleurella bouchardi (Davidson) from the Wenlock Limestone of Wenlock Edge, Shropshire, the cardinalia display a wide range of variation, particularly in the development of the cardinal process. The variation can be explained partly by ontogeny but in some extreme cases it is suggested that it reflects environmental control due to turbulent water conditions in an area of active reef growth. These conditions led mainly to the progressive inflation of the cardinal process to produce an optimum attachment surface for the diductor muscle bases, but in two specimens no cardinal process is developed. In these the muscle bases appear to have covered the notothyrial platform from the earliest growth stage, thus preventing the secretion of a cardinal process from a central strip of epithelium. The effect of this was to employ a maximum attachment area throughout ontogeny as an alternative to the production of a bulbous cardinal process.