Larval Descriptions of Two <i>Potimirim</i> (Holthuis, 1954) Species and Identification Key for the First Larval Stage of Amphidromous Shrimps From Brazil (Decapoda: Caridea)

ABSTRACT Amphidromy, a migratory pattern characterised by the development of planktonic larvae in estuarine waters and coastal zones while adults live and reproduce in freshwater, is observed in the life cycle of some species of caridean shrimps. In Brazil, amphidromous shrimps are represented by the families Atyidae, with the genera Atya Leach, 1816, and Potimirim Holthuis, 1954, and Palaemonidae, with the genera Macrobrachium Spence Bate, 1868, and Palaemon Weber, 1795. Accurate identification and understanding of the planktonic larvae of these shrimps are essential for ecological studies, population dynamics, taxonomy and phylogenetics of these species, as well as the understanding of the life cycle adaptation. This study aimed to investigate the potential of the morphology of the first larval stage (zoea I) for identifying amphidromous shrimp species occurring in Brazil, through the development of a dichotomous identification key. We described the zoea I of the two species of the genus Potimirim and conducted a bibliographic review to select all the studies describing the larvae of amphidromous shrimps found in Brazil. Based on outer and inner morphological characters as well as setation patterns of the first larval stage, we constructed a dichotomous key covering 14 taxa, of which 10 were identified at the species level. Despite the overall morphological similarity observed among the zoeae I, the combined use of diagnostic characters allowed reliable discrimination for all analysed larval descriptions. The illustrated plates and identification key provide a practical and standardised tool for species identification, contributing to planktonic studies, taxonomic research and the understanding of early life stages of amphidromous shrimps in Brazil.