Ultrastructure of coxal glands in the adult microtrombidiid mite Platytrombidium fasciatum (C.L. Koch, 1836) (Acariformes: Microtrombidiidae)
2007 - Volume: 47 Issue: 1-2 pages: 63-78
Morphology and ultrastructure of coxal glands of the adult microtrombidiid mite Platytrombidium fasciatum (C.L. Koch, 1836) (Acariformes: Microtrombidiidae) were studied by means of transmission electron microscopy and on semi-thin toluidine blue stained sections. The paired tubular coxal glands run along the axis of the body and occupy ventral and medial position. The cuticular excretory ducts of the coxal glands and the posterior alveolar salivary glands are joined together immediately after leaving the glands thus forming a common salivary duct (podecephalic canal) of each side of the body. Electron-microscopically, the coxal glands are found composed of two different kinds of tubes, which may be termed as a distal tube, giving rise to the excretory duct, and a proximal tube succeeding distal one and forming a basal (posterior) part of the organ. The distal tube goes backward up to the caudal end of the gland, where it makes several large loops directing forth and back, and then transforms into the proximal tube. The latter chaotically coils around the distal tube in anterior direction and finally terminates blindly at a distance of approximately 1/3 from the anterior termination of the gland. The cells of the tubes arrange around the central lumen as a rosette and are tightly adjoined each other leaving no conspicuous extracellular space between the adjacent cells of both the same and the opposite tubes. The cells of the proximal and the distal tubes are both provided with basal infolds (labyrinth) with mitochondria. The apical cell surface of the proximal tube bears long, tightly packed microvilli, whereas the apical plasma membrane of the distal tube remains flat and is armed with only scarce short protrusions. Lateral cell borders inside the gland are folded, and the adjacent cells are connected via septate desmosomes. Irregularly outlined nuclei of the both types of tubes are organized identically with rather small heterochromatin particles and a large nucleolus. Small Golgi bodies produce few small vesicles. No clear evidences of pinocytotic and exocytotic activity as well as vesicular transport across the glandular walls were observed. Nevertheless, the gland structure corresponds well to the organization of the transportation epithelia, and the coxal glands obviously take part in water excretion and ion/water regulation of the mite organism.
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