[The fine structure of the cortical zone in the gregarine Bothriopsides histrio (Eugregarinida: Actinocephalidae)].

Attached and non-attached trophozoites of the septate gregarine Bothriopsides histrio were found in the intestine of the freshwater beetle Acilius sulcatus. Circular folds in the border between proto- and deutomerites and longitudinal striation, running along the entire body of the parasite, were revealed in an optical microscope. Our studies have demonstrated that circular folds, forming a specific collar, are formed of ecto- and endocytes. The longitudinal striation is represented by overdeveloped folds developed by the epicyte and the ectocite. Numerous typical epicite folds were observed over the entire cell surface. Additionally, the symbiosis between gregarine cells and bacteria was revealed.