Rivulus kirovskyi, new species, from the central Amazon, lower rio Negro drainage, northern Brazil, is described. It is a member of an assemblage that includes R. amanapira, R. atratus, R. ornatus, R. rectocaudatus, R. romeri, R. tecminae, and R. uakti, and is diagnosed by a unique pattern of frontal squamation and a derived color pattern of the infraorbital region. Relationships of the new species with other taxa of the group are unclear at the present. It is similar to R. atratus, R. ornatus, and R. romeri in having an apomorphic reduction of anal-fin rays and by the absence of caudal spot in females, and similar to R. amanapira, R. rectocaudatus, R. romeri, R. tecminae, and R. uakti, by the absence of preopercular canal and dermosphenotic. Rivulus kirovskyi differs from all other species of the group by its unique color pattern of the caudal fin in males.

Key words: Systematics, rio Amazonas basin, rio Negro, Neotropical

Introduction

Rivulus Poey is a speciose assemblage of neotropical killifishes, including about 100 valid species, occurring in most river basins of Middle and South America between southeastern Mexico and northeastern Argentina (Costa, 2003a, in press). It comprises small to median sized species, about 22-110 mm SL, living in shallow freshwater streams and marginal pools (Costa, 1998, 2004, in press). The highest diversification of the genus is concentrated in northern South America, including river basins draining the Guianan Shield and the Amazonian lowlands. Costa (2003b, 2004) recognized a clade endemic to this area, diagnosed by a unique arrangement of frontal scales and the presence of an oblique infraorbital dark gray bar through chin, that includes R. amanapira Costa, R. romeri Costa, and R. uakti Costa, from the upper rio Negro basin, R. atratus Garman and R. ornatus Garman, widespread along central and eastern Amazon, R. rectocaudatus Fels & de Rham from the Peruvian Amazon, and R. tecminae Thomerson, Nico & Taphorn, from the upper rio Negro and upper río Orinoco basins. A new species of this clade, from the lower rio Negro basin, is herein described...

Full paper available at http://www.ufrgs.br/ni/vol2num1/vol2_1_09a12_rivulusLR.pdf.