Clusiomitidae, A New Family of Eocene Fossil Acalyptratae, with Revision of Acartophthalmites Hennig and Clusiomites Gen. Nov. (Diptera) †

SIMPLE SUMMARY: This study contributes to knowledge of the diversity of tertiary fossil flies of the group Acalyptratae. A new family Clusiomitidae is described on the basis of seven (four new) species from Baltic amber inclusions (Eocene, ca 48–34 Ma) belonging to two genera, Clusiomites gen. nov. and Acartophthalmites Hennig, 1965. Discovery of a new acalyptrate family in Baltic amber indicates an unusually rich diversity of this group in the so called “amber forest” covering a vast area of Europe in the Eocene climatic optimum. ABSTRACT: The Eocene Baltic amber fossil flies of the genus Acartophthalmites Hennig, 1965 (Diptera: Acalyptratae) are revised. Seven species are recognized and described or redescribed. Five species, A. crassipes sp. nov., A. luridus sp. nov., A. rugosus sp. nov., A. tertiaria Hennig, 1965 (type species) and A. willii Pérez-de la Fuente, Hoffeins et Roháček, 2018 are retained in Acartophthalmites while Clusiomites gen. nov. is described for two other species, C. clusioides (Roháček, 2016) comb. nov. (type species) and C. ornatus sp. nov. Relationships of these fossil taxa are discussed and, because they cannot be confidently placed in any known family of Diptera, a new family, Clusiomitidae, is established for them. Clusiomitidae is recognized as a family of Opomyzoidea, probably most closely allied to Clusiidae. These results again confirmed that the diversity of acalyptrate flies was very high in the Mid-late Eocene amber forest.