Excretory system ultrastructure of diphyllobothriid tapeworm Pyramicocephalus phocarum (Cestoda) with cytochemical and functional implication

Abstract

: The article describes the architecture and ultrastructure of the excretory system (protonephridial system) of the plerocercoid Pyramicocephalus phocarum (Fabricius, 1780), a parasite of the liver of the cod Gadus morhua Linneaus, 1758. The excretory system consists of cyrtocytes and a syncytial excretory epithelium, which forms the protonephridial funnels, the canal system, and the excretory bladder. Our immunocy-tochemical studies have shown that cyrtocytes are immunoreactive to α -tubulin, the protonephridial complexes are reactive to fibrillar actin. The excretory epithelium consists of differentiated apical cytoplasm specializing at secretion and reabsorption, and sub-merged cytons/perikarya. Architecture of the excretory system includes syncytial canals of various diameters and positions within the body. The 1 st and the 2 nd order canals form a complex three-dimensional peripheral network. The longitudinal central (main) excretory canals branch dichotomously at the posterior end of the body and flow into the excretory bladder. The main excretory canals possess a thick muscular wall innervated by the central nervous system. In addition, the ultrastructure of the excretory bladder, nephropore, terminal excretory pore are described. A close connection between the excretory and nervous systems occurs in the plerocercoid body. In the scolex, the main excretory canals and transverse excretory anastomoses pierce the brain, and underlie the transverse cerebral commissure. Neurites of the main nerve cords innervate the main excretory channels. Apart from this, there are unciliated sensory organs in the wall of the terminal excretory pore. The functional significance of the described structures is discussed. Based on the obtained ultrastructural and immunocytochemical data, we support the hypothesis of primary ultrafiltration through a molecular sieve of the glycocalyx, covering the weir ribs of protonephridia.