Four new species of Megalothorax Willem, 1900 are described and illustrated: M. tatrensis sp. nov., M. carpaticus sp. nov., M. hipmani sp. nov. from caves in Slovakia and M. draco sp. nov. from the Drǎcoaia Cave in western Romania. The species represent troglobiotic forms exhibiting different level of troglomorphy involving such features as larger body, elongated foot complex, antennae, mucro and body chaetae. The most pronounced troglomorphy is observed in M. hipmani sp. nov. and M. draco sp. nov. Species descriptions are completed with comparative tables of chaetotaxy of antennae and legs. Diagnostic table for all congeners and dichotomous identification key to the world species are provided. Distribution records of other Megalothorax species in Slovakia are added.

The paper deals with taxonomic revision of the genus Neelus Folsom, 1896. Two new species of the genus are described: N. koseli sp. nov. from caves of the eastern Slovakia and N. klisurensis sp. nov. from the Velika Klisura Cave in Serbia (Kosovo). Both species represent first known troglobiotic forms of the genus with distribution restricted to caves. They exhibit clear troglomorphic features not shared by other species of the genus: elongated unguis, larger body, elongated sensilla of Ant. IV segment, and others. Comparative table and dichotomous identification key for species of the genus are provided, remarks on distribution and ecology of species of the genus are added.

Two new species of the genus Neelus Folsom, 1896, N. cvitanovici sp. nov. and N. lackovici sp. nov., are described from caves of Croatia. N. lackovici sp. nov. exhibit marked troglomorphic features such as extremely elongated ungua and antennae, larger body among others. Descriptions are completed with comparative tables for chaetotaxy of antennae and legs. Diagnostic table for the congeners and identification key to the world species are provided. Distribution records of other Neelus species in Croatian caves are added. Threats of troglobiotic Neelus species in Croatia are discussed.

The new genus Spinaethorax, whose proposal is based on specimens of Megalothorax spinotricosus Palacios-Vargas & Sánchez, 1999, is given a new name combination and a redescription. The type species comes from two caves in Campeche State, México. A new combination is also suggested for Megalothorax tonoius Palacios-Vargas & Sánchez, 1999. The new genus is similar to Megalothorax Willem, 1900 and Neelus Folsom, 1896, but it clearly differs from all genera within family Neelidae by a peculiar combination of characters and the presence of some new features, e.g. globular sensillum on Ant. III, sword-like macrosetae on oral fold. A comparative table and an identification key for all Neelidae genera as well as some summary tables of antennae chaetotaxy and legs setation for type species are provided.

New species of Megalothorax Willem, 1900 from Dobšinská Ice Cave, Slovakia, M. dobsinensis sp. n., is described and illustrated. New species inhabits a cold habitat along an inversed temperature gradient at the cave entrance. M. dobsinensis sp. n. differs from other species of the genus by the lack of chaeta X on Ant. IV and by T-shaped inner chaetae of thoracic and abdominal sensory fields. Only two other species, M. tuberculatus Deharveng & Beruete, 1993 and M. sanctistephani Christian, 1998 lack chaeta X on Ant. IV. M. dobsinensis sp. n. differs from both species by chaetotaxy of antennae and abdomen. Summary tables of antennae and legs chaetotaxy and dichotomous identification key for species with smooth mucro are provided.