Biserova N.M., Mustafina A.R. 2015. Comparative midgut ultrastructure in three species of Tardigrada // Arthropoda Selecta. Vol.24. No.4: 373–385 [in English].
KEY WORDS: Eutardigrada, ultrastructure, intestine, enterocytes, glycocalyx, peritrophic membrane, membranous digestion, Halobiotus stenostomus, Richtersius coronifer, Milnesium tardigradum.
ABSTRACT. The ultrastructure and adsorption ability of the midgut in eutardigrades from a variety of marine, freshwater, and terrestrial ecosystems and with either phytophagous or zoophagous feeding habits, as well as having or lacking a capacity for anhydrobiosis have been studied. Differences revealed in the morphology of the intestine, the thickness of the intestinal wall, the nature of the folding of the apical and basal surfaces, intensification of adsorption ability and membranous digestion. It is shown that the maximum values of these attributes are characteristic for Milnesium tardigradum, large predators living in unstable conditions of drip of water bodies, capable to the long anhydrobiosis. These values of phytophagous moss-dwelling Richtersius coronifer are close to those of another phytophagous species Ramazzottius tribulosus. In zoophagous Halobiotus stenostomus (marine species, unable to anhydrobiosis), we identified significant differences in the ultrastructure and morphometric parameters of the intestine between the juvenile and adult stages of the animal. In juveniles (24-h age, did not feed), the digestion membrane surface was increased by 75 times that closely matches the data for other zoophages, Macrobiotus richtersi and Isohypsibius prosostomus. In the intestines of actively feeding adult H. stenostomus, we found the powerful development of peritrophic membrane; and morphometric parameters of increasing the membrane surface was significantly reduced (35). In addition, the enterocytes in the front and rear sections of the midgut revealed morphological and functional differences in the ultrastructure. The functional role of the peritrophic membrane in the digestive process is discussed. Our data indicate the existence of ultrastructural adaptations in the intestine of tardigrades with different food preferences and varying ability to rapid response to changes in the environment, in particular the ability to anhydrobiosis.