Helen’s twins in the Balkans: discovery of two new Paraptychoptera Tonnoir, 1919 species closely related to P. helena Peus, 1958, with systematic revision of the 'lacustris' group (Diptera, Ptychopteridae)

Ptychoptera castor Keresztes & Kappert, sp. nov. and P. pollux Keresztes & Török, sp. nov. both belong to the subgenus Ptychoptera (Paraptychoptera) Tonnoir (1919) and are described from boggy headwaters in the south Balkan area. These new species are closely related to the range-restricted P. helena Peus, 1958, which is known only from Oiti village, Mount Oeta, Phthioitis region, Greece and, together with P. lacustris, forms a morphologically well-defined unit in the subgenus Paraptychoptera. Based on cladistic analyses of 53 different morphological characters using the male antenna, wing, and genital structures, a general revision of the “lacustris” group is proposed with a dichotomous key of Paraptychoptera species.