On the taxonomy and biogeography of Potamon atkinsonianum (Wood-Mason, 1871) and Potamon (Potamon) emphysetum (Alcock, 1909)

The Himalayas are known to be a geologically young and dynamic mountain range hosting an endemic flora and fauna. To date, for freshwater crabs, one endemic subgenus within the genus Potamon, Potamon (Himalayapotamon) Pretzmann, 1966, has been described from the Himalayas. This subgenus includes two species, Potamon atkinsonianum (Wood-Mason, 1871) and Potamon emphysetum (Alcock, 1909). The taxonomic position of these two species is reconsidered. The subgenus Himalayapotamon is raised to generic level and its systematic and zoogeographic position is discussed. Based mainly on the morphology of the male copulatory system, Himalayapotamon belongs to the family Potamidae. It is more related to the Eurasian genus Potamon Savigny, and is distinct from the South-East Asian genus Potamiscus as well as from the Indian freshwater crabs of the family Gecarcinucidae. Zoogeographically Himalayapotamon appears to be an endemic genus related to Potamon, both genera presumably being isolated during the Miocene when the Gangetic waters were separated from the western Eurasian river systems. Further speciation occurred during glacial periods.