Some ultrastructural observations on the midgut epithelium of Isohypsibius augusti (Murray, 1907) (Eutardigrada)

Abstract

The midgut epithelial cells of the eutardigrade Isophypsibius augusti are organized into a convoluted monolayer. Only a single cell type could be distinguished although this cell type displayed considerable morphological variation. The midgut begins with crescent-shaped cells. More distally the cells are of variable height depending on the stored amount of nutritional material. No regenerative cells are present. Adjoining cells are held together by apical zonulae continuae. All the cells are characterized by a striated border, some basal infoldings, cytosis vesicles, numerous mitochondria, and abundant rough endoplasmic reticulum. Dictyosomes occur in small numbers. Ovoid or spherical inclusions (spherites), often concentrically laminated, are common. The cells, especially those along the middle part of the gut, are filled with large amounts of nutritional storage which includes polysaccharide material. The possible functions of the midgut in Tardigrada are discussed.

The fine structure of the midgut epithelium in Xerobiotus pseudohufelandi (Iharos, 1966) (Tardigrada, Eutardigrada, Macrobiotidae)

“…Therefore at the anterior end of the midgut epithelium of X. pseudohufelandi a group of cells forms a structure that we refer to as the epithelial ring. Cells of the epithelial ring correspond to crescent-like cells (midgut regenerative cells) described in some tardigrade species (Bertolani, 1970;Dewel and Clark, 1973;Greven, 1976;Ząbczyk, 2000;Rost-Roszkowska et al, 2011a). However, we did not observe their proliferation, a characteristic feature of midgut regenerative cells of invertebrates (Hakim et al, 2010;Nardi et al, 2010).…”

“…Up to now two kinds of cells have been described in the midgut epithelium of tardigrades: digestive cells that form the epithelium and crescent-like cells situated between the foregut and the midgut (Bertolani, 1970;Dewel and Clark, 1973;Greven, 1976;Kristensen, 1976;Pirch and Greven, 1994;Ząbczyk, 2000;Avdonina et al, 2007;RostRoszkowska and Poprawa, 2008;Rost-Roszkowska et al, 2011a). Fig.…”

“…The amount of reserve material (e.g. lipids, proteins, saccharides) in the tardigrade midgut cells increases to enable the survival of the animal in case of, for example, starvation or any other external stress factor (Greven, 1976;Pirch and Greven, 1994;Rost-Roszkowska and Poprawa, 2008). In Isohypsibius granulifer granulifer Thulin, 1928 (Eutardigrada) numerous structures with reserve material accumulate gradually in the cytoplasm of the midgut digestive cells as oogenesis occurs (RostRoszkowska et al, 2011a).…”

Ultrastructure of the digestive system of Ramazzottius tribulosus and Macrobiotus richtersi (Eutardigrada) in relationship with diet

“…As noted by Greven (1976) for Thulinius augusti (or Pseudobiotus megalonyx), the midgut surface is made wider by large folds of the gut wall. This pattern was present in R. tribulosus and M. richtersi.…”

“…In particular, detailed descriptions were made for two hypsibiids, namely Thulinius augusti (Murray, 1907) [or possibly Pseudobiotus megalonyx] and Isohypsibius prosostomus Thulin, 1928 (Greven 1976;Avdonina & Biserova 2003), and for one milnesiid, namely Milnesium tardigradum Doyère, 1840 (Dewel & Clark 1973 a, b, c;Dewel & Dewel 1979). Other papers have considered two other hypsibiids, Ramazzottius oberhaeuseri (Doyère, 1840) and Halobiotus crispae Kristensen, 1982 (Kinchin 1990;Eibye-Jacobsen 1996, 2001, one macrobiotid, Macrobiotus hufelandi Schultze, 1834 (see Shaw 1974;Walz 1975) and two heterotardigrades, namely echiniscid heterotardigrade Echiniscus viridissimus Péterfi, 1956(see Dewel et al 1988Dewel & Eibye-Jacobsen 2006) and halechiniscid Actinarctus doryphorus Schulz, 1935(see EibyeJacobsen 2001.…”