The endogean flora and fauna of European Russia, including those of the northwestern Caucasus, but excluding those of Crimea, presently comprise at least 389 species or subspecies (some still unidentified) from 229 genera (a few still unidentified), 150 families, 75 orders, 48 classes and 25 phyla, among which 96 species or subspecies represent presumed stygo-or troglobionts. The taxonomically most diverse phylum is Arthropoda which encompasses the bulk of the fauna, in particular due to crustaceans, beetles and collembolans. Whereas the troglofauna of northern Russia is completely devoid of such strongly cave-adapted animals, in the Urals, Cis-Urals and central Russia there are a few, but the greatest diversity of hypogean species in the region is observed in the northwestern Caucasus, in particular its maritime western part, as an "Ice Age" refugium of nemoral biota rich in karst.