Abstract
Three new species are described from the Neotropical region comprising the Cerrado savannas of the central Brazilian plateaus, which is among the most important biodiversity centres in the world. These species are considered closely related to Melanorivulus dapazi from the same region, with which they share the presence of a rudimentary interarcual cartilage and a dark reddish brown distal margin on the male anal fin. The group comprising Melanorivulus dapazi and the three new species is here named as the Melanorivulus dapazi species group. Melanorivulus ignescens sp. n., from the upper Rio Araguaia basin, is distinguished from all other species of the Melanorivulus dapazi group by the anal-fin colour pattern in males; Melanorivulus flavipinnis sp. n. and Melanorivulus regularis sp. n. from the Rio Paraguai basin are distinguished from all other congeners of the Melanorivulus dapazi group by the colour pattern of the caudal fin and number of scales in the longitudinal series, respectively. All the new species are further unambiguously diagnosed by unique combinations of morphological characters, including meristic and morphometric data, and colour patterns. This study reinforces the importance of using live colour patterns to diagnose species and species groups of the genus Melanorivulus, but also indicates that osteological characters may be informative for species diagnosis. This study confirms the high diversity of species of Melanorivulus in the central Brazilian Cerrado plateaus already reported in previous studies, indicating that endemic species are often restricted to short segments of a single river drainage.
Highlights
The region comprising the Cerrado savannas of central Brazil has been considered among the most important biodiversity hotspots in the world (Myers et al 2000), many organisms endemic to this region were insufficiently sampled and poorly known until recent years (Costa et al 2016)
Morphological characters indicate that all three new species here described are more closely related to M. dapazi than to other congeners, with these four species comprising the M. dapazi group
Species of the M. dapazi group share the presence of a dark red-brown distal margin on the male anal fin (Figs 1, 4, 6), a condition not found in other congeners
Summary
The region comprising the Cerrado savannas of central Brazil has been considered among the most important biodiversity hotspots in the world (Myers et al 2000), many organisms endemic to this region were insufficiently sampled and poorly known until recent years (Costa et al 2016). The greatest diversity among species of Melanorivulus endemic to the Cerrado is concentrated in the central-western Brazilian plateaus, which range in altitudes from 400 to 1,100 m above sea level (asl), in the Caiapó mountain range (Costa 2012) This area is drained by the upper tributaries of the Rio Araguaia, flowing north and belonging to the Amazonas–Tocantins river system, and the upper Paraguai and Paraná river basins, flowing southwest and south, respectively, and belonging to the Paraná–Paraguay–Uruguay river system. All the three new species are considered to be closely related to M. dapazi, endemic to the Paraguai basin, by all sharing a rudimentary interarcual cartilage and a dark reddish brown stripe on the distal margin of the anal fin in males (vs interarcual cartilage well-developed and never a similar stripe on the anal-fin distal margin; see Discussion below). This assemblage is hereafter called the M. dapazi species group and the three new species are described
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