Heterotricha Loew and allied genera (Diptera: Sciaroidea): Offshoots of the stem group of Mycetophilidae and/or Sciaridae?

Known species of the Heterotricha Loew Group and Pterogymnus Freeman are described, an d their systematic position is considered. Pterogymnus includes a single species from the Chilean Region. Nine genera (seven of them newly described) are recognised in the Heterotricha Group, which occurs in all zoogeographic Regions except the Nearctic and includes 17 living species, three from Eocene amber and probably Mangas exilis Kovalev from Cretaceous amber. These genera have sometimes been placed in Sciaridae or Diadocidiidae, but reassessment of their characters shows that they cannot belong to any currently recognised families of extant Sciaroidea. Both groups appear closer to Mesozoic forms presently assigned respectively to Antefungivoridae or subfamily Mangasinae of Bolitophilidae (Heterotricha Group) and Mesosciophilidae (Pterogymnus). These groups are thus considered to belong to the basal stock from which Mycetophilidae, Sciaridae and possibly some other modern families are derived. Following discussion of relationships with other Sciaroidea and between the taxa themselves, a tentative phylogeny of Sciaroidea is suggested.