The Pirabas Formation occurs in the states of Pará, Maranhão and Piauí, although it is better represented in the state of Pará (ROSSETTI; G6ES, 2004). Micropaleontology in the Pirabas Formation still has much to be studied, due to its great faunal diversity, especially with regard to ostracods. The present study deals with the taxonomy of the subfamily Cytherettinae Triebel aiming to identify the genera and species and assist in paleoenvironmental interpretations. The study area comprises Mine B-17 (CIBRASA), municipality of Capanema, Pará, where collections were made specifically in a profile subdivided into levels, from bottom to top, from BO to BIS. The 18 samples were processed and sorted (30g) in the polishing and microscopy laboratory of the CCTE/MPEG using the usual methods, and the best specimens were selected to be photographed in the Scanning Electron Microscope. This process allowed the identification of two genera of the subfamily under study: Cytberetta and Protocytheretta; and the recognition of the species Cytberetta aff. C. punctata, Cytheretta sp. and Protocytheretta sp. The quantitative and qualitative analysis of the fauna allowed the identification of 122 specimens of Cytheretta and 15 specimens of Protocytheretta, and the levels BO, B1A, B2A, B2 and B7A were the most abundant. Thus, these levels represent the phases of greater marine influence, since the genera studied are common in these environments; unlike the other levels, which represent more restricted environments. This may be related to modifications in environmental factors that occurred throughout the Miocene deposition period. Therefore, the importance of studying microfossils, especially those of ostracods, is one of the bases of paleoenvironmental reconstruction that contributes to paleoecological studies of the Pirabas Formation.
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