Confocal microscopy reveals uniform male reproductive anatomy in eriophyoid mites (Acariformes, Eriophyoidea) including spermatophore pump and paired vasa deferentia.

Male internal genitalia of eriophyoid mites comprise cuticle lined (anterior genital apodeme, genital chamber and ductus ejculatorius) and soft (paired vasa deferentia and single testis) organs. Three-dimensional reconstructions based on autofluorescence show that a thin-walled genital chamber is usually situated in a transverse plane and precisely copies the shape of the spermatophore. A thin vertical longitudinal plate (homologous to female longitudinal bridge) joins the genital chamber and ventral genital cuticle. The anterior genital apodeme is a separate vertical plate situated ahead of the genital chamber and provides a rigid support for it. The brightly autofluorescent ductus ejaculatorius starts from the posterior extremity of the genital chamber and goes backward. Proximally, the ductus ejaculatorius is tube-like, whereas distally, it is expanded into a sac. Confocal laser scanning microscopy observations on males, stained with phalloidin, indicate that the proximal ductus ejaculatorius is devoid of muscles whereas the distal ductus ejaculatorius possesses well-developed musculature (the "spermatophore pump"), appearing in 3D reconstructions as a hollow sphere with three apertures: one anterior and two posterior. Two thin-walled sausage-like vasa deferentia join the distal ductus ejaculatorius with a large single testis, each junction is encircled by a strong, ring-shaped muscle (musculus sphincter testiculodeferentis). Thin muscular fibers of the wall of the testis form a net-like pattern consisting of distinct polygonal cells. The topography of the male internal genitalia and musculature suggests that, contrary to previous observations, the spermatophore head might be extruded first and then the spermatophore stalk appears. The possible role of visceral and skeletal musculature, in the process of the expulsion of a spermatophore, is discussed.