Abstract
Charax awa sp. n. is herein described from the Rio Mearim, Rio Munim and Rio Turiaçu basins, three coastal river basins of northeastern Brazil located between the Rios Gurupi and Parnaíba basins. These have a complex and still poorly known biogeographic history. This region is ecologically extremely relevant since it comprises three of the main Brazilian biomes, as well as, transition zones between them: Amazônia, Brazilian Cerrado and Caatinga. Therefore, this area has faunal and floristic representatives of these three biomes, which makes it particularly relevant in terms of ecology, biodiversity and conservation. Charax awa sp. n. possesses a relatively small orbital diameter (22.1–28.5 % HL), what distinguishes it from most of its congeners, except from C. notulatus and C. caudimaculatus. It differs from C. caudimaculatus by a longer snout, and from C. notulatus by the number of scales around the caudal peduncle, as well as by the number of vertebrae. The new species herein described differs from its geographically closely distributed congeners, C. leticiae, C. niger, and C. pauciradiatus mainly by the relative horizontal orbital diameter. It is a “small-eyed” species. In addition, C. awa sp. n. can be distinguished from C. leticiae by having a maxilla extending to the vertical line posterior to the pupil, near the posterior orbital margin and by having a lower humeral spot distance. It can be distinguished from C. pauciradiatus by more scale rows from the pelvic-fin origin to the lateral line and more scale rows from the dorsal-fin origin to the lateral line and it differs from C. niger by having more transverse scale rows in space from the humeral spot to the supracleithrum. In addition, it differs from C. pauciradiatus and C. niger by the absence of bony hooks on anal and pelvic-fins rays of adult males.
Highlights
Characidae is the most species-rich family of Characiformes, comprising about 165 genera and more than 1.150 species, distributed along the river systems between southwestern Texas and Mexico in North America and Patagonia in South America (Nelson et al 2016; Eschmeyer et al.2017)
Some records of Charax for the coastal river basins of northeastern Brazil were made before the taxonomic revision made by Menezes and Lucena (2014): Martins and Oliveira (2011) recorded C. gibbosus for the Rio Mearim basin; Barros et al (2011) recorded Charax sp. for the Rio Itapecuru basin; Martins and Oliveira (2011) recorded Charax sp. for the Rio Pericumã basin and Rio Mearim basin
Charax can be distinguished from all other characid genera by the presence of a deep concavity on the latero-ventral portion of the cleithrum originating a relatively long posterior spiniform projection extending below pectoral-fin base; and an anterior shorter process oriented straight forward or either inclined or bent laterally (Lucena 1987, Mattox and Toledo-Piza 2012: fig 34, Menezes and Lucena 2014)
Summary
Characidae is the most species-rich family of Characiformes, comprising about 165 genera and more than 1.150 species, distributed along the river systems between southwestern Texas and Mexico in North America and Patagonia in South America (Nelson et al 2016; Eschmeyer et al.2017). The distribution of the genus is mainly concentrated in central and northern South America; there is no record for eastern Brazil and none of the valid species was assigned for the coastal river basins of northeastern Brazil by the recent taxonomic revision of the genus (see Menezes and Lucena 2014). Some records of Charax for the coastal river basins of northeastern Brazil were made before the taxonomic revision made by Menezes and Lucena (2014): Martins and Oliveira (2011) recorded C. gibbosus for the Rio Mearim basin; Barros et al (2011) recorded Charax sp. A new species of Charax is described from the Rio Mearim, Rio Munim and Rio Turiaçu basins, three coastal river basins of northeastern Brazil
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