Anchialine cave systems of the Yucatan Peninsula harbor diverse microbial communities adapted to perpetual darkness, oligotrophy and haloclines. Amplicon sequencing of 16S rRNA genes from 18 caves identified 847 OTUs, of which 34% showed less than 90% identity to any described species. Chemolithoautotrophic sulfur-oxidizing bacteria dominated at halocline depths, while methane-cycling archaea were enriched in deeper anoxic zones. Several taxa showed restricted distributions suggesting cave-specific endemism driven by hydrological isolation.

Halite nodules from the hyperarid core of the Atacama Desert were examined for preserved biosignatures using confocal laser scanning microscopy, Raman spectroscopy and stable isotope analysis. Cyanobacterial communities within fluid inclusions showed preservation of intact cell walls, pigments and diagnostic lipid biomarkers over millennial timescales. The preservation fidelity and mineralogical context provide a terrestrial analogue for evaluating halite deposits as priority targets in Mars sample return missions.

Three new troglobitic species of the amphipod genus Niphargus are described from cave systems in the Western Carpathians of Romania. Morphological and molecular phylogenetic analyses place the new species within the N. tatrensis species group. All three taxa display pronounced troglomorphic characters including eye and pigment reduction, elongated appendages and hypertrophied chemoreceptors. Distribution patterns suggest independent colonization events from surface-dwelling ancestors during Miocene karst formation.

This review synthesizes evidence on tardigrade survival under extreme conditions relevant to astrobiology, covering desiccation-induced cryptobiosis, radiation resistance, vacuum tolerance and results from space exposure experiments. Molecular mechanisms underlying extreme stress tolerance are reviewed, including the role of intrinsically disordered proteins, DNA repair systems and protective small molecules. The implications for panspermia hypotheses and the search for life on icy moons are critically evaluated.