Kotrba, Marion and Mathis, Wayne Neilsen. 2009. "The Internal Female Reproductive Tract of the Enigmatic Genus Risa (Diptera: Schizophora: Ephydroidea) and its Phylogenetic Implications." Proceedings of the Entomological Society of Washington, 111, (3) 627–640. https://doi.org/10.4289/0013-8797-111.3.627.
The internal female reproductive tract of Risa is characterized by a pair of short spermathecal ducts with no spermathecae, paired short accessory glands, and a large thimble-shaped strongly sclerotized ventral receptacle. This condition is identical with that in the ground plan of Ephydridae but differs from that of their next relatives, i.e., Camillidae and Diastatidae, regarding the shape of the ventral receptacle. It therefore corroborates the close relationship of Risa with Ephydridae either as its sister taxon or within that family.
