A new genus and species of Ephemeroptera, Astraeoptera cretacica gen. et sp. nov., is described from the Lower Cretaceous limestone of the Crato Formation (Brazil). The new taxon has the following diagnostic characters: veins MP₂ e CuA straight at their bases, MA branching in the apical half of wing length, CuA not forked, cubital field with longitudinal veins sub-parallel to CuA. It was compared with other adult mayflies worldwide, both fossil and extant, and could not be assigned to any known ephemeropteran family. In addition, holotypes of other two mayfly species were reanalyzed, resulting in taxonomical changes. A new description of the Costalimella zucchii Zamboni, 2001 holotype is provided, indicating its placement within Hexagenitidae, rather than Siphlonuridae, as previously proposed. We also reanalysed the holotype of Cratogenites corradiniae Martins-Neto, 1996, providing new and more accurate information about the species and confirming its junior synonymy to Protoligoneuria limai Demoulin, 1955. Our results indicate that the diversity of Crato Formation mayflies, both at species and family level, is greater than previously thought, confirming the predominance of hexagenitids among Cretaceous ephemeropterans.

蜉蝣新属新种Astraeoptera cretacica gen。等 sp. 11 月，是从克拉托组（巴西）的下白垩统石灰岩中描述的。新分类群具有以下诊断特征：脉MP ₂ e CuA 在它们的基部笔直，MA 在翼长的顶端一半分枝，CuA 不分叉，肘区纵脉与CuA 亚平行。它与世界范围内的其他成虫蜉蝣进行了比较，无论是化石还是现存的，并且不能归入任何已知的蜉蝣科。此外，对其他两种蜉蝣物种的正模标本进行了重新分析，导致了分类学上的变化。Costalimella zucchii 的新描述提供了 Zamboni, 2001 正模标本，表明它在六线虫科中的位置，而不是如先前提议的那样。我们还重新分析了1996 年Cratogenites corradiniae Martins-Neto的正模，提供了关于该物种的新的和更准确的信息，并确认了其与Protoligoneuria limai Demoulin, 1955 的次要同义词。我们的结果表明，Crato Formation 蜉蝣的多样性在物种和家族级别，比以前认为的要大，证实了白垩纪蜉蝣类中六元类的优势。