Structure of the midgut epithelium in four diplopod species: histology, histochemistry and ultrastructure

Abstract The middle region of the digestive system of millipedes, the midgut, is responsible for all processes connected with digestion, but also takes part in homeostasis maintenance thanks to the ability to activate many mechanisms which neutralize changes occurring at different levels of the animal’s body. Numerous millipede species are treated as bioindicators of the natural environment and they are exposed to different stressors which originate from external environment. To obtain all data on the functioning of midgut of millipedes as the barrier against stressors, it is necessary to have a precise and general description of the midgut epithelium. Members from four millipede orders were selected for the studies: Polydesmus angustus (Polydesmida), Epibolus pulchripes (Spirobolida), Unciger transsilvanicus (Julida) and Glomeris tetrasticha (Glomerida). The structure and ultrastructure of their midgut epithelial cells (the digestive, secretory and regenerative cells) were documented using transmission electron microscopy and histochemical methods. The obtained results have been compared and discussed to previous ones, to present the general and structural organization of the midgut in Diplopoda. Our studies revealed that the ultrastructure of all cells which form the midgut epithelium in millipedes is general for all the species studied up to now and it resembles the cell ultrastructure observed in Chilopoda and Hexapoda, including the digestive, secretory and stem cells.