Rivulus

[[Genus Rivulus]]

The killifish genus Rivulus Poey constitutes the most speciose and geographically widespread assemblage of aplocheiloid fishes. A great diversity in species of Rivulus has long been known from Central America and the northern part of South America, including river basins draining the Guyana Shield and the western portion of the Rio Amazonas basin (Costa, 2003, 2006). However, a rich diversity of species has only recently been reported for the central part of South America, including southern tributaries of the rio Amazonas (Tocantins, Araguaia, Xingu, and Tapajós) and the rio Paraná-Paraguay- basin (Costa, 1995a, 2005). Rivulus is still a poorly diagnosed genus, but it contains well-corroborated monophyletic units. This is the case for an assemblage formerly known as the Rivulus punctatus species group (Costa, 1995a), now considered to comprise the subgenus Melanorivulus (Costa, 2006), a well supported clade endemic to central South America. This subgenus comprises 18 species: Rivulus apiamici Costa, R. cyanopterus Costa, R. dapazi Costa, R. decoratus Costa, R. egens Costa, R. litteratus Costa, R. modestus Costa, R. paracatuensis Costa, R. parnaibensis Costa, R. pictus Costa, R. pinima Costa, R. punctatus Boulenger, R. rossoi Costa, R. rutilicaudus Costa, R. scalaris Costa, R. violaceus Costa, R. vittatus Costa, and R. zygonectes Myers. A new species of this clade, collected in the rio Caiapó drainage of the upper Rio Araguaia basin, is herein described.