Life stages of Brasilocaenis mendesi Malzacher, 1998 (Ephemeroptera: Caenidae) with redescription of male imago

Brasilocaenis mendesi was described by Malzacher in 1998 based on male imagos collected in Mato Grosso, Brazil. However, knowledge about the species is still limited, as the nymph, female, and egg remained undescribed. Based on specimens collected in the state of Pará, this study presents morphological variations not reported in the original description and provides the first descriptions of the female imago, egg, and nymph. As a result, it was observed that the styliger plate presents variations in the posterior margin, with deep emargination or subtle concavity, and a length between 0.09 mm and 0.12 mm. The forceps show variation at the tip, which can be shorter, subequal, or slightly longer than the plate. The female imago is differentiated by the projecting posterior margin of sternum IX. The chorion of the eggs is smooth, and the nymphs have dorsal microspines on the operculate gills, truncated sternite IX, and hind tarsal claws with approximately 14 denticles. A key to the nymphs of Brasilocaenis from Brazil is also proposed. These data expand morphological and taxonomic knowledge of the species.