Summary
A systematic electron microscopic investigation was undertaken to elucidate the regional differentiation of the protonephridial tubules of the freshwater planarian Bdellocephala brunnea. The excretory system consists of many independent protonephridia, each made up of the repeatedly branching “proximal tubules,” and highly tortuous “distal tubule.” The proximal tubules are composed of a simple ciliated epithelium except in the trunk which lacks ciliation. The cytoplasmic features of the ciliated cell closely resemble those of the flame cell, indicating highly active protein reabsorption by pinocytosis. Pinocytosis seems also active in the trunk of the proximal tubules and in the distal tubule, resulting in cytoplasmic vesicles of typical appearance. Salient features of the distal tubule cell are the increased density of the cytoplasmic matrix and the presence of many basal compartments of cytoplasm with mitochondria, a pattern common to many epithelia with osmoregulatory function. The morphology and possible functions of the planarian protonephridium are discussed in comparison with the vertebrate nephron.
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References
Ernst SA, Ellis RA (1969) The development of surface specialization in the secretory epithelium of the avian salt gland in response to osmotic stress. J Cell Biol 40:305–321
Hyman LH (1951) The invertebrates: Platyhelminthes and Rhynchocoela. Mc Graw-Hill Book Co Inc, New York, Vol 2
Ishii S (1962) Electron microscopic observations on the planarian tissues. I. A survey of the pharynx. Fukushima J Med Sci 9:51–73
Ishii S (1980) The ultrastructure of the protonephridial flame cell of the freshwater planarian Bdellocephala brunnea. Cell Tissue Res 206:441–449
Klima J (1961) Electronenmikroskopische Studien über die Feinstruktur der Tricladen (Turbellaria). Protoplasma 54:101–162
Maunsbach AB (1966) Absorption of I125-labeled homologous albumin by rat kidney proximal tubule cells. A study of microperfused single proximal tubules by electron microscopic autoradiography and histochemistry. J Ultrastruct Res 15:197–241
McKanna JA (1968) Fine structure of the protonephridial system in planaria II. Ductules, collecting ducts, and osmoregulatory cells. Z Zellforsch 92:524–535
Pedersen KJ (1961a) Studies on the nature of planarian connective tissue. Z Zellforsch 53:569–608
Pedersen KJ (1961b) Some observations on the fine structure of planarian protonephridia and gastrodermal phagocytes. Z Zellforsch 53:609–628
Silveira M, Corinna A (1976) Fine structural observations on the protonephridium of the terrestrial triclad Geoplana pasipha. Cell Tissue Res 168:455–463
Wetzel BK (1962) Contributions to the cytology of Dugesia tigrina (Turbellaria) protonephridia. Breese SS (ed) Proc 5th Int Congr Electron Microscopy. Academic Press, New York, Vol 2, Q-10
Wissig SL, Graney DO (1968) Membrane modifications in the apical endocytic complex of ileal epithelial cells. J Cell Biol 39:564–579
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The author is deeply indebted to Professor T. Oosaki and Assistant Professor T. Hikichi for their revision of the manuscript
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Ishii, S. The ultrastructure of the protonephridial tubules of the freshwater planarian Bdellocephala brunnea . Cell Tissue Res. 206, 451–458 (1980). https://doi.org/10.1007/BF00237974
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DOI: https://doi.org/10.1007/BF00237974