The Skeleton and Musculature of the Male Genitalia in Platypezidae (Diptera)

Abstract

The musculature of the male genitalia of Platypezidae (Diptera) is described for the first time. The hypandrium in members of the subfamilies Platypezinae and Callomyiinae belongs to two different structural types. The Platypezinae type is basal and shows great similarity to that in Diptera Orthorrhapha, while the Callomyiinae type is derivative and very similar to that in most Diptera Cyclorrhapha. The hypandrium of the Platypezinae type is trough-shaped and represents a transitional state in the formation of a tubular hypandrium of the Callomyiinae type. The formation of a tubular hypandrium could have led to drastic shortening of the phallus, while the orientation of the phallotrema changed from dorsal in Platypezinae to ventral in Callomyiinae. The pregenital sclerites and also the musculature of the hypandrial complex in Platypezinae demonstrate an evolutionarily more advanced state of the characters. Additional evidence is provided to support the hypothesis that the gonopods were incorporated into the hypandrial structure in Cyclorrhapha. The presence of dedicated muscles in the pregonites suggests that in Platypezidae these sclerites are gonopod derivatives rather than hypandrium outgrowths.