Abstract
Hyphessobrycon nicolasi is described from the Uruguay River basin in the Mesopotamian Region, Entre Ríos, Argentina. The new species can be distinguished from all congeners by the presence of a well-defined oblique and marginal black stripe on each lobe of the caudal fin. Other characters defining H. nicolasi are the possession of 1-3 teeth with 3-10 cusps on maxilla; outer premaxillary row with 2-3 small teeth, with 5 or 7 cusps; iv-vi, 27-36 anal-fin rays; 33-36 scales on the longitudinal series; two vertical dark spots on the humeral region; dorsal and anal fins dappled in black and base of caudal fin bearing conspicuous black spot; and the presence of bony hooks on the rays of dorsal, anal and caudal fins of the mature males.
Highlights
The genus Hyphessobrycon Durbin includes more than 100 valid species, occurring from Mexico and Central America to the Mar Chiquita Lagoon in Buenos Aires, Argentina and reaching its highest richness in the Amazon basin (Lima et al, 2003; Miquelarena & López, 2006; Bertaco et al, 2007)
All measurements are expressed as percentage of standard length (SL), except for head measurements, which are expressed as percentage of head length (HL)
Within characids Hyphessobrycon is diagnosed by the combined possession of incomplete lateral line, naked caudal fin, presence of adipose fin, two series of premaxillary teeth, and second infraorbital not contacting the preopercle inferiorly (Eigenmann, 1917; Géry, 1977)
Summary
The genus Hyphessobrycon Durbin includes more than 100 valid species, occurring from Mexico and Central America to the Mar Chiquita Lagoon in Buenos Aires, Argentina and reaching its highest richness in the Amazon basin (Lima et al, 2003; Miquelarena & López, 2006; Bertaco et al, 2007). Authors that have recently addressed the systematics of the genus are unanimous in pointing out that the group is not well defined and its monophyly is yet uncertain (e.g., Bertaco & Carvalho, 2005; Bertaco & Malabarba, 2005; Carvalho & Bertaco, 2006; Bertaco et al, 2007). During field trips to tributaries of the Uruguay River in Entre Ríos province, Argentina, the authors collected a new species of Hyphessobrycon that presents unique characters among the members of the genus
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