With the objective of improving the knowledge about Ephemeroptera in the North region of Brazil, the group’s first survey was carried out for the metropolitan region of Santarém, Pará, Brazil. The specimens analyzed were collected from 2019 to 2020 in 27 aquatic environments distributed in the region. The nymphs were captured in the streams with aquatic entomological nets, in addition to manual collection on the substrates. Adults were collected using light traps and flight intercept traps. To complement the inventory, a bibliographic survey of species previously recorded in the area was carried out. For this, the Taxonomic Catalog of Fauna of Brazil, the website Ephemeroptera in South America and scientific articles were consulted. As a result, eight families, 23 genera and 31 species/morphospecies were recorded for the region, with 13 new records for Pará and 19 for the metropolis of Santarém. This study demonstrates the relevance of surveys for the knowledge of biodiversity and for understanding the geographic distribution of taxa.

A new species of Tricorythopsis is described, illustrated and diagnosed based on nymphs from Pará state, Brazil. Tricorythopsis similis sp. nov. is related to Tricorythopsis rondoniensis (Dias, Cruz & Ferreira) based on abdominal terga III–VII with acute tubercles medially located on posterior margins, and by the absence of the transversal line on operculate gill. However, the new species can be identified by the following combination of characteristics: general coloration yellowish brown, with blackish and purplish marks irregularly distributed; maxillary palp 1-segmented; segment II of labial palp shorter than segment I and longer than segment III; femora and tibiae with margins covered by long, pectinate setae; tarsal claws with 4 to 5 marginal denticles and 4+2 very small, submarginal denticles. This is the first species of Tricorythopsis recorded from Pará state.