ИСТИНА

Traditionally, it is accepted that the coelomic system of articulate brachiopods is composed of the perivesciral cavity, forming an extension to the mantle, and the canal system of the lophophore (Hyman, 1959). The lophophore contains the coelomic canals: great and small brachial canals. In Linguliformea the coelomic spaces were described in the esophagus connective tissue (Pross, 1980). In Novocrania anomala, a central coelomic canal surrounds the esophagus and connects with the small brachial canals (Blochmann, 1892). Until now, there has been no information as to whether any related cavities are present in articulate brachiopods. Detailed investigation of the coelomic system in Hemithyris psittacea revealed that articulate brachiopods possess a periesophagal coelom that surrounds the esophagus. It is isolated from the perivisceral cavity but connects with the small brachial canals. The periesophagal cavity is crossed by irregular septa. The lining of the periesophagal coelom includes cells of two types: epithelial and myoepithelial cells. Both are monociliary. Some epithelial cells have long processes extending along the basal lamina. Perhaps these cells function as podocytes. The myoepithelial cells have the basal myofilaments. The periesophagal coelom forms protrusions penetrating the connective tissue of the body wall above the mouth and the connective tissue surrounding the esophagus. The coelomic lining of the canals above the mouth consists of flattened epithelial cells. The canals of the esophagus connective tissue form a three-dimensional network. Three types of canals are distinguished. The external canals are close to the cavity of the periesophagal coelom. Their coelomic lining consists of the epithelial cells and the podocytes. The wall of the middle deep canals is formed by both epithelial and myoepithelial cells with the smooth muscle fibers running along the longitudinal axis of the esophagus. The deepest canals lose the lumen; they are filled with the muscle cells surrounded by basal lamina. Their smooth muscle fibers are circular. What is the function of the complicated system of canals in the connective tissue of the esophagus? The canals perform a dual function, the first of which may be excretion. The podocytes have not been found in brachiopods before, so the site of ultrafiltration has been uncertain. The gut of brachiopods is surrounded with a thick layer of loose semi-fluid connective tissue, which plays the role of the blood sinus. At the same time, the coelomic lining of the periesophagal coelom contains the podocyte-like cells. So, the ultrafiltration may take place in these very areas. Articulate brachiopods lack an anus, hence antiperistalsis is necessary for the release of faecal pellets through the mouth. Perhaps the thickened muscle wall formed by the middle deep and the deepest canals may serve this purpose. References: Hyman, L.H., 1959. Smaller Coelomate Groups. 516-609 in Hyman, L.H., The Invertebrates. McGraw-Hill, New York. Blochmann, F., 1892. Die Anatomie von Crania anomala (Muller). 1-65 in Blochmann, F., Untersuchungen uber den Bau der Brachiopoden. Gustav Fischer, Jena. Pross, A., 1980. Untersuchungen zur Gliederung von Lingula anatina (Brachiopoda). Archimerie bei Brachiopoden. Zoologische Jahrbucher, abteilung fur Anatomie und Ontogenie der Tiere 103, 250– 263.