Non-marine ostracods are environmental proxies widely used in Quaternary environmental and climatic reconstructions. In South America (Neotropical Region), extant Limnocytheridae is the third most diverse family, with Limnocythere species typically inhabiting hyposaline to mesosaline waters. The South American Transitional Zone (SATZ), is defined across South America by arid-semiarid climate, holding the Argentinean section five endemic Limnocythere species, representing highest diversity of Limnocythere and the speciation role of this transitional area. This study analyses the diversity, paleoecological traits and distribution of Quaternary Argentinean Limnocythere, describing Limnocythere perseverans sp. nov. from Laguna Llancanelo basin, Salina del Bebedero and Laguna Runtuyoc (Argentinean SATZ), providing a dichotomous key for the 13 Quaternary species found in Argentina. The new species differs from L. cusminskyae (Neotropical Region, humid Chaco-Pampean) and L. staplini (Nearctic Region), in valve morphology (valve shape and hinge structure) and ecological requirements. Limnocythere perseveranssp. nov. prefers sodium-chloride, sulfate or chloride-sulfate waters, segregated from L. cusminskyae living in sodium, bicarbonate-rich waters, and L. staplini found in bicarbonate-depleted waters. These differences highlight its value to reconstruct changes in salinity and water chemistry. The morphological similarities among these three species open questions on biogeographical aspects of aquatic ecology. Further research is necessary to assess whether these species evolved from a shared ancestor or are an example of morphological convergence derived by the adaptation to similar ecological pressures within the Neotropical and Nearctic regions.