Morpho-functional variety of the coxal glands in cheyletoid mites (Prostigmata). I. Syringophilidae

•The coxal gland of the quill mites comprises proximal and distal tubes followed by the “violet” and “green” portions.•The proximal and distal tubes are characterized by apical membrane invaginations associated with pinocytotic canals.•The “violet” gland portion indicates reabsorptive activity and produces secretory granules of unknown nature.•The terminal “green” portion produces a proteinaceous secretion and might functionally substitute lost salivary glands.•At the base of the excretory duct, there have been found structures probably regulating the dilation of the duct lumen.

The anatomy and fine structure of the osmoregulatory coxal glands have been investigated in the parasitic quill mites, Syringophylopsis fringilla (Fritsch) and Torotrogla cardueli Bochkov & Mironov (Syringophilidae). In both species, tubular coxal organs are the only pair of propodosomal glands, whereas in most Prostigmata, several acinous (salivary) glands are also present entering a pair of podocephalic canals, which are continuations of the coxal glands' excretory ducts.In the adults and tritonymphs of the quill mites, the coxal glands show the same basic morphology with slight differences in their packing mode between the studied species. A filtering sacculus is absent. Each gland consists of a long tubular gland body comprising 4 to 6 longitudinal trunks and a cuticle-lined excretory duct continuous into the podocephalic canal. The gland body is composed of 4 morphologically distinct regions: proximal and distal tubes followed by the two granule-containing regions denoted as the “violet” and “green” gland portions.Electron microscopy showed the epithelium of the proximal and distal tubes to be rich in deep apical membrane invaginations associated with branched pinocytotic canals or vacuoles, especially extensive in the distal tube. A number of large mitochondria are concentrated basally to maintain ionic and water transport. The enlarged penultimate “violet” portion is composed of high epithelial cells that show certain endocytotic activity and also produce a large amount of uniform secretory granules derived from numerous small Golgi bodies. The terminal “green” portion produces dense protein-like inclusions and might functionally substitute lost salivary glands. The fine structure of the podocephalic canal is also thoroughly described and compared to the information available in the literature.