Abstract
Abstract A new species of Xenurobrycon isdescribed from tributaries of the rio Tapajós, Pará, Brazil. It is diagnosed from all congeners by the dark color of the posterior half of both caudal-fin lobes, the presence of infraorbitals one, two, and three, the presence of a set of lamellar processes on eighth principal caudal-fin ray of mature males, the presence of bony hooks similar in size or decreasing posteriorly on last unbranched and first 9-12 branched anal-fin rays of mature males, the presence of only conical teeth on both jaws, the lack of the adipose fin and the presence of 15-18 predorsal scales. The description of the new species increases the number of species in Xenurobrycon to six. An updated key to the species of the genus is provided.
Highlights
The Xenurobryconini (Characidae: Stevardiinae) traditionally comprises seven inseminating genera (Weitzman & Fink, 1985; Weitzman & Menezes, 1998): Argopleura Eigenmann, Chrysobrycon Weitzman & Menezes, Iotabrycon Roberts, Ptychocharax Weitzman, Fink, Machado-Allison & Royero, Scopaeocharax Weitzman & Fink, Tyttocharax Fowler, and Xenurobrycon Myers & Miranda Ribeiro
The later addition of Chrysobrycon restricted the definition of the Xenurobryconini to the presence of a single pouch scale with or without hypertrophied radii in adult males, an ambiguously optimized character in the phylogenetic hypothesis by Weitzman & Menezes (1998), giving little support to the new composition of the group
Standard length (SL) is presented in mm and other measurements are expressed as proportions of SL, except for subunits of head which are expressed as proportions of head length (HL)
Summary
The Xenurobryconini (Characidae: Stevardiinae) traditionally comprises seven inseminating genera (Weitzman & Fink, 1985; Weitzman & Menezes, 1998): Argopleura Eigenmann, Chrysobrycon Weitzman & Menezes, Iotabrycon Roberts, Ptychocharax Weitzman, Fink, Machado-Allison & Royero, Scopaeocharax Weitzman & Fink, Tyttocharax Fowler, and Xenurobrycon Myers & Miranda Ribeiro. The monophyly of this tribe was originally proposed by Weitzman & Fink (1985), based on sexually dimorphic characters. The recent study by Thomaz et al (2015), questioned the monophyly of the Xenurobryconini, since their data strongly refuted Chrysobrycon (nested within the Stevardiini) and Argopleura ( an incertae sedis taxon) as members of the tribe, as previously proposed by Weitzman & Fink (1985), Weitzman et al (1994) and Weitzman & Menezes (1998).
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