An overview of the Hexagenitidae (Ephemeroptera) from the Crato Formation (Aptian, Lower Cretaceous) of Brazil, with the description of a new species

Among mayflies, the Hexagenitidae is the most common family of the Cretaceous, including in the world-renowned Crato Formation (Aptian) of northeastern Brazil. However, most of the Crato mayfly fauna was described based on nymphs, which, due to their ontogenetic development, may present numerous continuous characters. As a consequence, many unclear taxa have been described, and their taxonomic position needs to be re-evaluated. We here present a checklist and revision of some previously described species from the Crato Formation and the description of new specimens. We propose a new species, Protoligoneuria heloisae sp. nov., based on a previously described adult erroneously referred to within Oligoneuriidae. Further adult specimens of Hexagenitidae are here described in detail, presenting new morphological data and variations that were, up to now, unknown for Hexagenitidae of the Crato Formation. Lastly, we briefly discuss the genus Cratohexagenites. Our new findings further add to the taxonomical and morphological diversity of the adult mayfly fauna of the Crato Formation.