BIOLOGIYA MORYA, 2004, Vol. 30, No. 2, pp. 120-130

Ultrastructure of the blood system of the phoronid Phoronopsis harmeri Pixell, 1912. 2. The main vessels

© 2004 E. N. Temereva¹, V. V. Malakhov²

¹Institute of Marine Biology, Far East Branch, Russian Academy of Sciences, Vladivostok 690041;
²Biological Department, Moscow State University, Moscow 119899

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Ultrastructure of the wall of the main blood vessels of the phoronid Phoronopsis harmeri is described. The walls of the lophophoral and left lateral vessels consist of myoepithelial cells of the coelomic lining (peritoneal cells), a thin basal lamina, and incomplete endothelial lining. In the head region of the body, the wall of the medial vessel consists of myoepithelial cells of the coelomic lining (peritoneal cells), a basal lamina, and true muscular endothelial cells. The anterior part of the medial vessel functions as the heart. In the anterior part of the body, the medial vessel wall consists of five layers: external nonmuscular coelothelium, a layer of extracellular matrix, internal muscular coelothelium, an internal layer of extracellular matrix, and incomplete endothelial lining. The complicated structure of the medial vessel wall may be explained by the superimposition of the lateral mesentery on the ordinary vessel wall.

Key words: phoronids, ultrastructure, blood system, metamorphosis.