A new species of the seasonal killifish genus Moema (Cyprinodontiformes: Rivulidae) from the Piraí watershed in the Southwest Amazon basin

Abstract Moema, a genus of the Rivulidae family, currently comprises 20 valid species. Most of these species inhabit temporary pools in the Amazon basin and only one species is found in the upper Paraguay basin. A new member of this genus from the upper Río Madeira drainage is here described. Males of the new species differ from all congeners by the combination of a color pattern consisting of oblique, sometimes chevron-like, irregular rows of red and light blue double-dots on body; dark yellowish to golden pectoral fins with no visible markings; and a stripe pattern on the ventral section of caudal fin with a very narrow black marginal line, intermittent or even absent. The existence of infrageneric species groups within Moema, the geographic distribution and taxonomic aspects of the species present in the Ríos Mamoré and Iténez/Guaporé rivers drainages, and the observation of intraspecific aggression between males and amphibious lifestyle in the new species are discussed.