Male and female of Chilenomyia paradoxa are described. An outstanding autplesiomorphy of the male hypopygium, even as compared to Diptera in general, is apparently the presence of two pairs of well developed gonocoxites. The anterior pair of large, simple lobes is homologous with laterosternite IX of other chironomid males and with gonocoxite IX of the females. The posterior pair, consisting of gonocoxites + gonostyli, is enclosed between the anterior lobes and corresponds to the clasper apparatus of other Chironomidae. The male clasper of Chironomidae is hence evidently a derivative of sternite X and not of sternite IX as hitherto assumed. A further indication of this is the wellknown intimate connection between the claspergonocoxites and sternapodeme X. However, in Chilenomyia the sternapodeme forms a simple semicircular arch ending in sharp points deep into the cavity of the gonocoxites, while in other chironomids the sternapodeme is firmly connected with the anterodorsal margin of the gonocoxites. The Chilenomyia pattern is probably an autapomorphy. Another autapomorphy is displayed by the subapically inserted gonostyli which have rotated through 90° so that the normally frontal surface becomes directed dorsad, meaning that each gonostylus forms a clasper together with the apical end of the gonocoxite. This and supporting evidence lead to the conclusion that Chilenomyia deserves a new subfamily, Chilenomyiinae, which forms the sister group of a monophyletic group comprising all other chironomid subfamilies except Telmatogetoninae.