ИСТИНА

Concerning brachiopods, detailed ultrastructural data of the lophophore are restricted to the studies of the tentacles. We studied the ultrastructure of lophophoral coelomic lining in articulate brachiopod Hemithiris psittacea. The coelomic system of the lophophore consists of large and small canals; both extend along each brachium and end blindly at its tip. Small canal gives rise to blind branches into each tentacle. The lophophoral coelothelium consists of two types of cells, epithelial-muscle and peritoneal cells, and exhibits different types of organization that are known in Bilateria: from primitive epithelium consisting only of epithelial-muscle cells to pseudostratified myoepithelium. Lophophoral coelothelium forms musculature and blood vessel wall of the brachia and tentacles. The lophophoral blood vessel runs in the extracellular matrix of the septum that separates the large and small canals. In the lophophoral vessel, the upper wall consists of epithelial-muscle cells, whereas the lower wall is formed by peritoneal cells. Inner lining of the vessel consists of amoebocytes that do not form a true endothelium. Lophophoral vessel gives rise to blind branches into each tentacle. The wall of lophophore is highly muscular and contains both longitudinal and transverse muscles. As the spirolophe lophophore of H. psittacea is supported only by short crura, we assume that coelomic system of lophophore participates in retention of lophophore by regulation of hydrostatic pressure of the coelomic liquid.