A new species of freshwater amphipod belonging to genus Hyalella is described from a peatbog at high altitudes (3,650 to 4,400 m above sea level) in the Puna region (Salta province, northwestern Argentina). The new species can be distinguished from other hyalellid species by the following combination of characters: dorso-posterior flanges on pleonites I–III; palp on maxilla 1 reaching almost half of distance between base of palp and base of setae on outer plate, and two papposerrate setae on the inner margin of inner plate of maxilla 2; propodus of gnathopod 1 hammer-shaped, inner face with seven serrate setae; propodus of gnathopod 2 ovate; male uropod 1 without curved seta on inner side of inner ramus; ramus of uropod 3 shorter than peduncle; six pair of sternal gills on pereionites II–VII.
A detailed morphological description and illustrations of the new species are provided. In Argentina, the new species represents the third record for the genus at altitudes greater than 2,000 m a.s.l., after H.kochi and H.fossamancinii (Dos Santos et al. 2008, González 2003), and the first record above 4,000 m a.s.l. Some comments about distributional and ecological aspects of the new species are included. With this new species, the number of Hyalella species known from Argentina and Falkland Islands (Islas Malvinas) rises to 12.
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