Two new species of the subterranean amphipod genus Stygobromus (Amphipoda: Crangonyctidae) from Siberia, with new data on Stygobromus pusillus (Martynov) and remarks on morphology and biogeographic relationships

Two new species of the subterranean amphipod genus Stygobromus are described from groundwater habitats in Siberia: Stygobromus mikhaili n. sp. from a spring in the Central Altay Mountains and Stygobromus anastasiae n. sp. from two non-freezing springs in South Pribaikalye in the Irkutsk area. Additional taxonomic details of the previously described S. pusillus (Martynov) from Teletskoye Lake, also in Central Altay, are illustrated based on syntype material. Utilization of SEM has revealed a tiny structure on antenna 2 that appears to be a new character, and may prove useful in future analyses. Descriptions of the two new species raise the total number of described species in the genus Stygobromus to 134, but four or possibly five have been found in the Palearctic region outside North America. However, it is likely that continued exploration of subterranean groundwater habitats in Siberia and other parts of the Palearctic will reveal additional new species of Stygobromus and provide more insight into the origin and geographic distribution of this large, northern hemisphere, subterranean freshwater amphipod genus. Careful evaluation of taxonomic affinities of the new species and comparison with previously described congeners should provide further insight into the biogeographic history of Stygobromus.