The genus Hyalella is endemic to the North and South America. There are currently 14 species described in North America and the Caribbean. For a long time, it had been assumed that different populations of these animals represented a single species, Hyalella azteca (Saussure, 1858). However, molecular analyses have demonstrated H. azteca sensu lato to be a complex of multiple species, so some species that occur in the United States have been mistakenly identified. Our aim in this paper was to describe a new species of Hyalella, found in Oklahoma, USA. The new species can be differentiated from the others, mainly because it presents serrated setae in the maxilla 2, because it does not have flanges on the surface of the body, presents the palm of the gnathopod 2 of the same size as the distal-posterior margin of the propodus, by shape and number of setae on the uropod 3 and telson. The description of this new species of Hyalella increases to 15 the number of species of the genus for the USA. It is important to understand the diversity of Hyalella with consideration of their possible role as bioindicators of environmental quality, and further consideration of their conservation status, and especially for species known from a single spring.
Keywords: Crustacea, North America, new species, Hyalella.