A new species of the Phalloceros harpagos species complex (Cyprinodontiformes: Poeciliidae) from the middle and lower Uruguay River floodplains

Phalloceros mimbi sp. nov. is described from specimens collected in the floodplains of the middle and lower Uruguay River in Uruguay (Río Negro and Salto Departments) and Argentina (Entre Ríos Province). This species belongs to the P. harpagos species complex and is diagnosed by the following unique combination of characters: 1) presence of a symmetric hood-like structure located immediately anterior to the urogenital papilla in females, 2) absence of large papillae at the mandibular symphysis of large adult females, 3) possession of well-developed hooks positioned in distal portion of gonopodial appendices of males and4) lateral spot usually present in both sexes. To date, P. mimbi has not been found coexisting in sympatry with other Phalloceros species. The geographically closest species is P. caudimaculatus, who differs from P. mimbi by the absence of hooks in gonopodial appendix in males. Two of the three known populations of P. mimbi are relatively protected from the main threats to the species. However, conservation initiatives should consider its presence and ensure that it receives the necessary attention; considering that its global distribution occupies less than 200.000 km2 and its occurrence area represents less than 10% of the national territory it must be considered a priority for conservation and an Threatened Species for the species list of Sistema Nacional de Áreas Protegidas (SNAP) of Uruguay.