CHYROMYIDAE (DIPTERA) FROM THE GALAPAGOS-ISLANDS, ECUADOR - 3 NEW SPECIES OF APHANIOSOMA BECKER

Three new species of the genus Aphaniosoma Becker are described from t he Galapagos Islands, Ecuador: Aphaniosoma arenicolum Wheeler, n. sp. from the islands of Espanola, Isabela, Rabida, Santa Cruz and Santa Fe ; Aphaniosoma galamarillum Wheeler, n. sp. from the islands of Isabela and Santa Cruz; and Aphaniosoma rabida Wheeler, n. sp. from the islan d of Rabida. These species are the first members of the family Chyromy idae described from the Neotropical Region. Aphaniosoma arenicolum app ears to be closely related to a group of southern Nearctic species. Ap haniosoma galamarillum is the probable sister species to the Hawaiian species A. minutum Hardy. The affinities of A. rabida are unknown base d on present knowledge of the genus. Ancestors of the three species pr obably arrived in three separate colonization events via rafting by ad ults or larvae or as aerial plankton. The source area of these ancesto rs cannot be determined at present because there is no phylogenetic hy pothesis about relationships between the species of the genus and beca use there has been little collecting on the west coast of Central and South America, the most likely source area. Male postabdominal structu re in the genus Aphaniosoma is briefly discussed and some errors and o missions in previously published treatments of chyromyid terminalia ar e clarified.