The fine structure of the female reproductive system of Zorotypus caudelli Karny (Zoraptera)

The general structure of the female genital system of Zorotypus caudelli is described. The ovarioles are of the panoistic type. Due to the reduction of the envelope (tunica externa) the ovarioles are in direct contact with the hemolymph like in some other insect groups, Plecoptera included. The calices are much larger in Z. caudelli then in Zorotypus hubbardi and their epithelial cells produce large amounts of secretions, probably protecting the surface of the eggs deposited on the substrate. Eggs taken from the calyx bear a series of long fringes, which are missing in the eggs found in the ovariole, and in other zorapteran species. The long sperm of Z. caudelli and the long spermathecal duct are likely related to a sexual isolating mechanism (cryptic female choice), impeding female re-mating. The apical receptacle and the spermathecal duct - both of ectodermal origin - consist of three cell types. In addition to the cells beneath the cuticle lining the lumen, two other cell types are visible: secretory and canal cells. The cytoplasm of the former is rich in rough endoplasmic reticulum cisterns and Golgi complexes, which produce numerous discrete dense secretory bodies. These products are released into the receiving canal crossing the extracellular cavity of secretory cells, extending over a series of long microvilli. The secretion is transported towards the lumen of the apical receptacle of the spermatheca or to that of the spermathecal duct by a connecting canal formed by the canal cells. It is enriched by material produced by the slender canal cells. Before mating, the sperm cells are enveloped by a thick glycocalyx produced at the level of the male accessory glands, but it is absent when they have reached the apical receptacle, and also in the spermathecal duct lumen. It is likely removed by secretions of the spermatheca. The eggs are fertilized at the level of the common oviduct where the spermathecal duct opens. Two micropyles at the dorsal side of the equator level possibly facilitate fertilization. The presence of these two micropyles is a presumably derived feature shared with Phasmatodea. The fine structure of the female reproductive system of Z. caudelli does not allow to assess the phylogenetic position at the present stage of knowledge. The enlarged calyx and the temporary presence of long fringes on the eggs are potential autapomorphies of Z. caudelli or may indicate relationships with other Zorotypus species.

► Zoraptera is one of the most enigmatic orders of insects.
► The female reproductive system of a Zorotypus species is described for the first time in detail.
► The results are discussed with respect to the systematic position.
► Affinities with Phasmatodea are suggested.