AVDONINA, A.M.; Vladimir State Pedagogical University: Particular qualities of digestive system organization of Isohypsibius sattleri (Richters, 1902) (Tardigrada: Eutardigrada) with remarks about cuticle

Many authors described the fine structure of various eutardigrade species (Dewel, Clark, 1973, Shaw, 1974, Greven, 1975, Dewel, Dewel, 1979, Dewel, Nelson, Dewel, 1993, Eibye-Jacobsen, 1996, 1997 and others). The subject of present research is the study of digestive tract sections, cuticle and cuticle-muscular contacts of Isohypsibius sattleri (Eutardigrada) by transmission electron microscopic method. The collected specimens were fixed in a 1.5% glutaraldehyde (with 0.1 M cacodylate buffer added, pH 7.2) with preliminary immersion in a 1% acetic acid solution (10 minutes) to prevent the contraction. Postfixation was in a 1% osmium tetraoxide solution. The thickness and construction of multi-layer cuticle are showed in the different parts, the ultrastructure of dorsal and ventral gibbosities is considered. The gibbosities are made by the epicuticle, procuticle have many vacuoles. Subcuticle layer contain large quantity of lipid drops. The specific pattern of digestive systems organization is revealed. The folds functioning as valves at the transition from pharynx to esophagus are discovered. Earlier similar structure was registered for Isohypsibius prosostomus. The formations have the adaptive nature. The midgut having minor windings without large folds is wider than the foregut. The epithelial cells with the brush border form the central part of midgut. The hindgut is lined by a cuticle and has entodermal origin. Nearly the cloacal opening the muscles go to the cuticle resembled the usual cuticle-muscular contact.