Simple SummaryIn this study, we implemented a multifaceted approach, coupling phylogenetic, phylogeographical and demographic analyses together with a morphological characterization to depict the genetic patterns ofHeleobia atacamensis, an endangered species scattered in isolated and semi-isolated but dynamic habitats of the Atacama Saltpan. We focused on snails obtained from Peine and Tilomonte, two peripherical localities, which were compared with topotypes specimens. The range extension of the species also allowed us to reassess its conservation status. Molecular analyses showed that snails from Peine and Tilomonte belong toHeleobia atacamensis. We also discovered genetic structure in the saltpan, represented by six genetic clusters, besides morphological differences between populations. Since the observed pattern is common for other freshwater species restricted to desert aquifers worldwide, our results represent findings applicable to analogous systems. The species, listed as Critically Endangered at regional level in 2014, was reassessed as Endangered. For an eventual management plan, we suggest incorporating the genetic information obtained here.AbstractEvaporitic ecosystems of the Atacama Desert contain a rich endemic fauna, including mollusk species. A recent study performed in the freshwater snailHeleobia atacamensis, endemic to the Atacama Saltpan, revealed a strong interdependence of genetic patterns with climatic fluctuations and landscape physiography. The species is currently listed as Critically Endangered at regional scale and as Data Deficient on the International Union for Conservation of Nature (IUCN) Red List. Here, we studied genetic diversity and demographic history of several populations of the species occurring on a connectivity gradient, including snails from new peripherical localities (Peine and Tilomonte), which were compared with topotype specimens. In addition, we reassessed the conservation status using the IUCN Red List categories and criteria considering species-specific idiosyncrasy. Phylogenetic and phylogeographical analyses indicated that snails from Peine and Tilomonte belong toH. atacamensis. We discovered significant differentiation in shell morphology, which was generally greater in geographically isolated populations. We also inferred six genetic clusters and a demographic expansion congruent with the wet periods that occurred at the end of the Pleistocene. Considering the highest risk category obtained,H. atacamensiswas reassessed as Endangered at regional scale. Future conservation plans should consider the genetic assemblages as conservation units.