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

Three new species of the genus Aphaniosoma Becker are described from the 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 island of Rabida. These species are the first members of the family Chyromyidae described from the Neotropical Region. Aphaniosoma arenicolum appears to be closely related to a group of southern Nearctic species. Aphaniosoma galamarillum is the probable sister species to the Hawaiian species A. minutum Hardy. The affinities of A. rabida are unknown based on present knowledge of the genus. Ancestors of the three species probably arrived in three separate colonization events via rafting by adults or larvae or as aerial plankton. The source area of these ancestors cannot be determined at present because there is no phylogenetic hypothesis about relationships between the species of the genus and because there has been little collecting on the west coast of Central and South America, the most likely source area. Male postabdominal structure in the genus Aphaniosoma is briefly discussed and some errors and omissions in previously published treatments of chyromyid terminalia are clarified.