the Arabika Submarine Depression, all these facts point to the possibility that karst systems in Arabika could have originated in response to the Messinian salinity crisis (5.96–5.33 Ma) when the Black Sea (Eastern Paratethys) could have almost dried up, as did the adjacent Mediterranean, where the dramatic sea level drop of ~1,500 m is well established. Biology The biocenosis of Krubera-Voronja is composed of more than 12 species of arthropods of several groups, such as pseudoscorpions, spiders, opiliones, crustaceans, springtails, beetles and dipterans. Krubera-Voronja cave is inhabited by endemic species, including four springtails discovered during the CAVEX Team expedition of 2010: Anurida stereoodorata, Deuteraphorura kruberaensis, Schaefferia profundissima, and Plutomurus ortobalaganensis; the last of these is the deepest terrestrial animal ever found on Earth, living below the cave entrance. The beetle Catops cavicis inhabits Krubera-Voronja cave and also several caves around the Ortobalagan Valley. The subterranean amphipod crustacean Kruberia abchasica caught by Gennady Samokhin in August 2013, during dives in the siphon 'Dva Kapitana', dwells at the deepest part of the Krubera Cave (at the depth of −2,175 metres). History of exploration Early exploration At the beginning of the 20th century, Arabika was visited by French speleologist Édouard-Alfred Martel, who published several works about the massif. In 1909–10 Russian karst scientist Alexander Kruber, a founder of the study in Russia, performed some field studies in Arabika. He published his observations in a series of Arabika-specific papers and several monographs. During the subsequent 50 years no special studies were undertaken of the karst and caves in the region, although the karst of Arabika was referred to in many works dealing with regional geology and hydrogeology. 1960s In the early 1960s, Georgian geographers led by Levan Maruashvili began exploring caves in the high sector of the massif. Among several other caves, they made the first exploration of an open-mouthed 60 m shaft in the Ortobalagan Valley and named it after Alexander Kruber. The first explorers were stopped by impassable squeezes at −95 m in a meandering passage which led off from the foot of the entrance shaft. The cave remained largely neglected over the next 20 years, although occasionally visited by cavers from various caving clubs. Before 1980 there were no caves deeper than known in Arabika. 1980s The new era in cave explorations in the Arabika Massif began in 1980 when the Kyiv Speleological Club, led by Alexander Klimchouk, started exploring caves