Klastostachys reflexa, a new genus and species combination in the Harpellales, is established herein based on Stachylina reflexa, which was described in 1988. This gut fungus was found attached to the peritrophic matrix of small bloodworms, Cryptochironomus sp. (Chironomidae), in the Rocky Mountains of Colorado, USA. Klastostachys resembles Stachylina, a genus common in Chironomidae, but the unbranched thalli of Klastostachys disarticulate and disperse with the trichospores remaining attached to their generative cells. This manner of dissemination is unusual among Harpellales, being noted also for Carouxella spp., but members of that genus have zygospores attached at one pole to the zygosporophore (Type IV), whereas Klastostachys zygospores are medially attached to the zygosporophore at right angles (Type I).