Abstract Preliminary histological analysis showed that the ovaries in Nannochorista neotropica are composed of numerous ovarioles of panoistic type. In the ovaries of adult females each ovariole consists of a terminal filament, vitellarium and pedicle while a germarium is absent. Morphological observations supported by simple histochemical tests revealed the presence of multiple nucleoli in the oocyte nucleus. The appearance of multiple nucleoli suggests that the extrachromosomal amplification of ribosomal DNA may take place in the oocytes of Nannochorista. The results show that in the structure of the ovariole and the course of oogenesis nannochoristids share noteworthy derived features with boreids, but differ significantly from all other mecopterans. These findings indicate the possible monophyly of an assemblage comprising the Nannomecoptera, Neomecoptera and Siphonaptera.