ИСТИНА

Brachiopods are a relict group of marine invertebrates that first appeared in the early Cambrian (Hyman 1959). Some organ systems of recent brachiopods especially their blood systems are still poorly known. Researchers have published a few studies on the general anatomy of the circulatory system of brachiopods in the late nineteenth and early twentieth centuries (Hancock 1859; Blochmann 1892, 1900; Schaeffer 1926). The investigation of the fine structure of the blood system is restricted by a few studies about the main heart (Martynova and Chaga, 1997) and tentacle vessels (Storch and Welsch, 1976; Reed and Cloney, 1977). We have studied the anatomical and ultrastructure of the blood system rhynchonellid brachiopod Hemithyris psittacea ЗДЕСЬ НАДО ДАТЬ АВТОРА ВИДА. Our anatomical studies showed that the main heart is located on the dorsal side of the stomach behind the attachment of the gastroparietal mesentery to the stomach. The main heart gives rise the anterior and the posterior dorsal vessels. The anterior dorsal vessel runs forward from the main heart along the dorsal surface of the stomach and the esophagus. At the surface of the stomach it splits into two pairs of the vessels of the digestive diverticula. At the esophagus the anterior dorsal vessel gives rise the braches into the sinuses of the periesophageal coelom. At the circumoral region the anterior dorsal vessel splits into two lophophoral vessels running along each brachium. Each lophophoral vessel goes along the small coelomic canal and gives blind branches into each tentacle. Posteriorly to the main heart, the posterior dorsal vessel divides into two dorsal vessels, which then bifurcate to form a pair of dorsolateral and a pair of ventrolateral vessels. The dorsolateral vessels run along the lateral stomach sides; pass on the left and the right gastroparietal mesenteries; go along the funnels of the anterior nephridia; and form a network of gonad vessels in the dorsal mantle. The ventrolateral vessels run along the left and the right ileoparietal mesenteries, supply posterior nephridia with blood, and give rise to a network of ventral gonad vessels in the ventral mantle. The mantle vessels end blindly on the periphery of the gonad. We found the vesicle-like accessory heart on the lateral vessels behind the nephridial funnels, close to the gonad vessels. Accept of the structured vessels the blood system contains the two sinuses: the periesophageal sinus replacing in the septa of the periesopageal ceolom and the circumintestinal sinus running around the gut. We studied the fine structure of the wall of the ventro-lateral, dorsal, lophophoral, tentacle and gonad blood vessels and the accessory heart using the transmission electron microscopy. In all cases the wall consists of the outer coelomic epithelium, the extracellular matrix (ECM) and inner amoebocyte lining. The ECM consists of basal lamina contouring the basal parts of coelomic cells and fibro-reticular layer. The amoebocytes are not connected by desmosomes and lacks of the basal lamina. Thus, they cannot be considered as a true epithelium. The mantle gonad vessel is very specific because its wall functions as the genital lamella that give rise gametes. The coelomic epithelium of the dorsal, lophophoral and tentacle vessels represents by the podocyte-like cells with numerous interdigitating pedicels. The structure of the main heart wall was studied using the transmission electron microscopy, cytochemistry, and confocal laser scanning microscopy. The main heart attaches to the dorsal vessel by the narrow tube-like stalk that grade into the large sac-like part in the coelomic cavity. The outer coelomic epithelium of the sac wall consists of two types of cells. The first type is epithelia-muscle podocyte-like cells with long thick muscle processes forming strong muscle network in the heart wall and thin interdigitading pedicels. The second type is peritoneal cells containing numerous inclusions and abundant rough endoplasmic reticulum. Amoebocytes contain convoluted nucleus, numerous inclusion. The fibro-reticular layer of the ECM containing scattered collagen fibers is located between the basal lamina coelomic epithelium and amoebocytes. In a systolic condition the ECM is very convoluted contouring the basal parts of coelomic cells together with their pedicels, the amoebocytes closely cuddle together. In a diastolic condition, the coelomic epithelium stretches; the ECM becomes thin, and the basal lamina straightens. The regions of the basal lamina between the pedicels of podocytes turn out to face the coelomic space. Since these amoebocytes are not fastened together by desmosomes, the gaps between amoebocytes, where the ECM directly faces the heart cavity, widen. In this case we supposed the ultrafiltration liquid from the heart cavity to the coelom. So, the main heart may perform a dual function: blood propulsion and excretion. The wall of the tube-like stalk consists of the epithelia-muscle cells without pedicels and long thick muscle processes. We found the nerves in this part of the main heart. The wall of the periesophageal sinus contains the podocyte-like cells. Thus, we proposed two sites of ultrafiltration. The first site replaces in a compartment of the ceolomic system that consists of the two interconnected parts: periesophageal coelom and the small coelomic lophophoral canals. The second site replaces in the perivisceral coelom that is isolated of the periesophageal and lophophoral coelom. The use of an antibody against ɑ-tubulin and phalloidin for actin reveals the presence of two types of cells in the outer wall of the sac-like part of the heart. Cells of first type exhibit strong ɑ-tubulin-like immunoreactivity and are not stained for phalloidin. Cells of second type are podocyte-like cells, which have weak reaction against ɑ-tubulin, but are strongly stained for phalloidin. Methods of cytochemistry allow to describe the organization of the tube-like portion of the heart. It is composed of columnar epithelial non-muscular cells, which are underlined by muscles cells. These cells are located in the connective tissue of the tube and form its musculature. Muscle cells are oriented in different direction, mostly obliquely with respect to the longitudinal axis of the tube. ɑ-tubulin-like immunoreactive cells are scattered at the basal portion of the epithelium of the tube. Thin neurites of the ɑ-tubulin-like immunoreactive cells form sparse nerve net around the tube-like portion of the heart. Among epithelial cells of the heart tube, there are some cells that can be visualized with staining against ɑ-tubulin. Their apical surface form swelling and contact the lumen of the trunk coelom. These cells can be apparently regarded as sensory.