Freshwater Amphipod Crustaceans of Patagonia, Argentina: Two New Species of Hyalella Smith, 1874 with an Identification Key for the Genus

The genus Hyalella (Amphipoda, Hyalellidae) includes over 100 species, exclusively inhabiting freshwater ecosystems across South, Central, and North America. In southern South America, pristine natural environments are rapidly declining due to the exploitation of natural resources and changes in land use. These activities exert significant pressure on aquatic ecosystems, degrading water quality. Within these ecosystems, the macroinvertebrate fauna, particularly the diversity of Hyalella, remains understudied and highly vulnerable. This paper describes two new species from hydrographic basins near glaciers in western Patagonia, Argentina, specifically in the provinces of Santa Cruz and Neuqun, south of 36 S latitude. Both species belong to the patagonica complex, named after Hyalella patagonica. They share key characteristics such as a long palp on maxilla 1, a hatchet-shaped propodus on male gnathopod 1, a male inner ramus of uropod 1 without sexual setae, uropod 2 with a long fine seta on the peduncle, epimeral plate 1 rounded and plates 23 slightly acuminate posterodistally, and sternal gills on pereonites 37. Hyalella domuyo sp. nov. is distinguished by its antenna 2 being much longer than antenna 1, a slight constriction on the palp of maxilla 1, pereopod 4 coxa bearing a thin serrate seta in the posterior cavity, pereopod 7 basis with three short subdistal setae on the outer surface, and telson with 13 thin setae on the apical margin. Hyalella rioturbiensis sp. nov. differs from other species in the patagonica complex by its unique combination of characters, including a row of plumose setae on the peduncular segment 4 of antenna 2, more than 12 serrate setae on the inner face of the male propodus of gnathopod 1, tiny plumose setae on the dorsal surface of coxa 4, uropod 3 peduncle bearing three strong setae, one being flagellate-type, uropod 2 peduncle slightly shorter than the outer ramus, and a telson apex with three main setae. Comments on the distribution of these new species are provided. With the addition of these species, the known number of Hyalella species from Argentina and the Falkland Islands (Islas Malvinas) rises to 18, including three species complexes: H. curvispina, H. patagonica, and H. kochi. A key to the Hyalella species of Argentina is also presented.