Revision of the Microphorella acroptera species group and establishment of the Microphorella arcana species group (Diptera: Dolichopodidae sensu lato: Parathalassiinae)

The Microphorella acroptera species group is revised and the Microphorella arcana species group is established. The M. acroptera species group includes M. acroptera Melander and M. tubifera Melander, plus the following 14 newly described species: M. acuminata sp. nov., M. bifida sp. nov., M. compacta sp. nov., M. convoluta sp. nov., M. cornuta sp. nov., M. elongata sp. nov., M. maculata sp. nov., M. paracroptera sp. nov., M. serpentina sp. nov., M. sinuosa sp. nov., M. subacroptera sp. nov., M. tenuis sp. nov., M. triangulata sp. nov. and M. trochanterata sp. nov. Four distinct lineages within the M. acroptera species group are recognized. The M. arcana species group includes the following three newly described species: M. arcana sp. nov., M. gilaensis sp. nov. and M. ovata sp. nov. Both species groups occur only in the western Nearctic Region. The M. acroptera species group is recorded from southeastern Alberta south to Washington, western Oregon and southern California, east to Nevada and northwestern Arizona. The M. arcana species group is known from California and central Arizona. The distribution of each species is mapped and a key to males of both species groups is provided, including an update to the Nearctic Microphorella species group key published by Cumming & Brooks (2022).