Species possessing mvo: Protaphorura bakhchisaraica sp. nov. and P. salsa sp. nov. from two peculiar habitats: xerothermic bushes in Ukraine (Crimea) and a salt lake shore in Russia (South Siberia) are described. Two other species with this organ, Protaphorura ianstachia Yosii, 1972 and P. stiriaca (Stach, 1946), are redescribed, discussed and their lectotypes designed. An identification key to all known Protaphorura species having mvo is given. The structure and arrangement of the organ is applied as a sharp diagnostic character at the species level.