Rivulus xinguensis
Costa, 2010
Two new species of the Rivulus urophthalmus group from the Tocantins and Xingu river drainages, eastern Brazilian Amazon (Cyprinodontiformes: Rivulidae)Rivulus tocantinensis, new species, from the middle section of the Tocantins River drainage, and R. xinguensis, new species, from the lower Xingu River drainage, eastern Amazonas River basin, northern Brazil, are described. Both species are missing the well-defined marginal yellow stripes on the caudal fin present in adult males of all other species of the R. urophthalmus group. Rivulus tocantinensis is distinguished from all other species of the R. urophthalmus group in having wide dark orange stripes on the flank and large dark orangish brown blotches on the middle of the caudal fin in males, and the absence of dermosphenotic bone or sometimes represented by a rudimentary ossification; R. xinguensis differs from other species of that group in having fewer scales in the longitudinal series.
Wilson J. E. M. Costa
Ichthyological Exploration of Freshwaters, 21 (1): 79-85, 2010.