The caves located in the Frasassi Gorge, Marche region (central Italy) contain numerous sulfidic habitats that represent hotspots of subterranean biodiversity. They host unusually rich and diverse invertebrate communities that display specific adaptations to cave life. As in other sulfidic subterranean ecosystems discovered worldwide (Movile Cave in Romania, Ayyalon Cave in Israel, Melissotrypa Cave in Greece, and Tashan Cave in Iran), primary production in Frasassi's sulfidic sections is fuelled by chemoautotrophic sulfur-oxidizing microorganisms. Conversely, few animals are present in cave sections where trophic resources are scarce and dependant on surface input, such as upper fossil passages and cave pools filled with percolation water from the epikarst. A single vertebrate species, the salamander Speleomantes italicus (Dunn, 1923), and numerous species of invertebrates have been identified in Frasassi's sulfidic sections, of which 22 are stygobionts and 5 are troglobionts (including 12 endemic species). Specific adaptations to the extreme environmental conditions encountered there, such as highly toxic sulfide levels and low pH, have been identified in some species. Notably, symbioses observed between amphipods of the genus Niphargus and filamentous sulfur-oxidizing bacteria belonging to the genus Thiothrix may help them better cope with sulfide toxicity.