Shatrov A.B. 2008. [Electron-microscopic organization of the midgut and excretory organ in the adult water mite, Teutonia cometes (Koch, 1837) (Parasitengona: Hydrachnidia: Teutoniidae) and its evolutionary implication] // Invertebrate Zoology. Vol.4 (for 2007). No.2: 195–208 [in Russian, with English summary].

Zoological Institute of the Russian Academy of Science, Universitetskaya emb., 1, 199034 Saint-Petersburg Russia. E-mail: chigger@mail.ru

KEY WORDS: water mites, Teutonia cometes, Teutoniidae, midgut, excretory organ, morphology, ultrastructure.

ABSTRACT: Midgut and excretory organ of the adult water mite Teutonia cometes (Koch, 1837) (Hydrachnidia: Teutoniidae) were investigated by means of transmission electron-microscopy and in semi-thin sections. The midgut is represented by a weakly divided blind sac with uniform walls throughout the gut and may contain nutritive (food) substrate in the form of homogenous electron-clear globules. A single-layered midgut epithelium consists of the single-type entodermal digestive cells of various shape and size, which form bulbous protrusions into the midgut lumen. Specialized secretory cells were not obviously observed throughout the midgut epithelium. Large nuclei with lobed envelope have large nucleolus, which may sometimes be counted in a number of two or three. Apical surface of the digestive cells forms scarce microvilli, among which pinocytotic pits and vesicles fusing together and immersing into the cell are formed in mass. Intracellular digestion is realized in this water mite species. The cells contain electron-dense secondary lysosomes (heterolysosomes), the agents of intracellular digestion, residual products in the form of variously granular vacuoles or substance, as well as reserve nutritive as lipid inclusions and glycogen granules. Residual masses are released into the midgut lumen, and their further path is unknown. The excretory organ is a thin-walled weakly divided entodermal sac bearing scarce branched and curved microvilli on the apical cell surface. The cells possess dense ground cytoplasmic matrix and contain mitochondria, lipid and glycogen inclusions as well as sparse electron-dense inclusions of unknown origin. The nuclei are greatly similar with those of the digestive cells. In the lumen of the excretory organ waste nitrogen products are crystallized and concentrated, which are disposed together with scarce electron-dense bodies.

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