Hyalella is widely distributed in the Americas. Until the present moment around 30 species have been identified. Hyalella curvispina Shoemaker is treated as synonynous with Hyalella pernix (Moreira) due to the very strong similarities found in both species: they have in common an outstanding curved spine on the inner ramus of uropod 1 of the male. This is considered the main characteristic of H. curvispina. With the species already known and the synonymy treated here a total of 29 species of Hyalella is reached. It would seem that H. pernix is the most widespread species in Brazil and in South America as a whole.