The morphology and systematics of the clam shrimp Platyestheria gen. nov. abaetensis (Cardoso) (Crustacea, Spinicaudata) from the Lower Cretaceous of the Sanfranciscana Basin, southeast Brazil

Abstract

New specimens of the clam shrimp ‘Pseudestheria’ abaetensis Cardoso, 1971 (Spinicaudata) are described. The material was collected from the Quiricó Formation (Lower Cretaceous of the Sanfranciscana Basin), at the same locality as the type series of the species. The carapaces are very large, oval and elongated, with anteriorly located and slightly projected umbo, straight dorsal margin, with flattened growth bands and 15–20 serrated growth lines. Details of the microscopic structure of the carapace were analysed under scanning electron microscope for the first time, disclosing a unique reticular pattern of ornamentation. This species is similar to some Early Cretaceous taxa from South America, Africa and China. Yet, the peculiarities in the shape and ornamentation of the carapace support its reassignment to a new genus (Platyestheria gen. nov.), within the Superfamily Eosestherioidea. In addition, an energy-dispersive X-ray spectroscopy analysis of the multiple stacked growth bands revealed that the valves are enriched in calcium and phosphorus, similar to those of modern spinicaudatans. Minor amounts of silicon, iron and aluminium suggest that the carapaces were preserved partly through the input of ions from the environment during the diagenesis.