Resumo em Inglês:

ABSTRACT The Neotropical mayfly genus Massartella Lestage, 1930 has long been regarded as species–poor, despite recent evidence indicating that its diversity, especially in the Atlantic Forest, is underestimated. Here, we describe Massartella aurora sp. nov. from the Serra do Brigadeiro State Park, Minas Gerais, Southeastern Brazil, based on nymphs, male and female imagos, subimagos, and eggs. The new species is diagnosed in the adult stage by the presence of a single small forewing spot at the IMA bifurcation, 20–21 cross veins in the male forewing costal region, abdominal terga with narrow outer and broad inner oblique bands, and penial lobes with a broad rounded apical projection lacking a dorsal groove. Nymphs are distinguished by maxillary palp II bearing 17–19 robust pectinate setae, femora with numerous robust spatulate setae on the dorsal surface, and gills on abdominal segments I–VI with numerous pigmented tracheae. Eggs have a chorion with regular ridges forming a hexagonal pattern and circular KCT–type attachment structures. Synchrotron X–ray microtomography was used to generate three-dimensional digital models of the nymph and male genital structures, documenting a reproducible methodological workflow that complements traditional morphology and scanning electron microscopy. The description of M. aurora sp. nov. represents the first step toward resolving the hidden diversity of Massartella in the Atlantic Forest and provides a formal name for a lineage relevant to ongoing taxonomic and integrative studies.