A new Australian genus and family of Diptera (Nematocera: Perissommatidae).

Abstract

A new dipterous family (Perissommatidae) is erected to accommodate the genus Perissomma, gen. nov., with its two species, P. fusca, sp. nov., and P. mcalpinei, sp. nov. The genus possesses a considerable number of unusual morphological and biological features including, in the adult, a complete, V-shaped, mesonotal suture; an unusual wing venation, with median cell and costal "ambient vein"; and lateral division of the eyes into completely separate, dorsal and ventral components. P. fusca breeds during the winter months in autodigesting fungi (Boletus granulatus) which occur in large numbers in pine forests near Canberra. The larva is eucephalic and peripneustic, and pupation occurs within a puparium formed from the unmodified larval skin. The species apparently survives through dry weather by means of the prepupa and puparium which show structural adaptations to resist desiccation. Comparison with other Nematocera suggests that Perissomma belongs in the section Bibionomorpha and its immature stages show some resemblance to those of the Scatopsidae. However, no grounds can be found for including it in any known family, and it appears to be a specialized relict of a primitive bibionomorph stock.