Velebit
There are hundreds of "holes" on Velebit. It has the largest and deepest caves in Croatia. The three-part "Lukina jama" cave is 1392 m deep, making it one of the deepest caves in the world, and the deepest in southeast Europe, while the "Slovačka jama" is 1320 m. What makes it unique is that it is completely vertical, steepest in the world. At the bottom of the pothole is a water course or siphon with branches that are still unexplored. A kind of leech was discovered in the pothole, which has been ascertained to represent a new species, genus and family; it has been named "Erpobdella mestrovi".
Krubera Cave
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).