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Acta Parasitologica, Vol.46, No. 4, 2001, 280-292
Swiderski Zdzislaw (1)(2), Ndiaye Papa Ibnou (3)(4), Miquel Jordi (3), Tkach Vasyl (1), Marchand Bernard (5), Chomicz Lidia (2), Grytner-Ziecina Barbara (2), Sereda Michal J. (1) - Ultrastructural study of the embryonic development of the anoplocephalid cestode Anoplocephaloides dentata, an intestinal parasite of Arvicolidae rodents. II. Differentiation and cellular organisation of the oncosphere.

(1) W. Stefanski Institute of Parasitology, Polish Academy of Sciences, 51/55 Twarda Street, 00-818 Warszawa, Poland; (2) Department of General Biology and Parasitology, Medical University of Warsaw, Chalubinskiego 5, 02-004 Warszawa, Poland; (3) Laboratori de Parasitologia, Facultat de Farmacia, Universitat de Barcelona, Av. Joan XXIII s/n, E-08028 Barcelona, Spain; (4) Laboratoire de Parasitologie, Departement de Biologie Animale, Faculte des Sciences, Universite Cheikh Anta Diop, Dakar, Senegal; (5) Laboratoire Parasites et Ecosystemes Mediterraneens, Faculte des Sciences et Techniques, Universite de Corse, BP 52, 20250 Corte, France

During oncospheral differentiation in Anoplocephaloides dentata the degeneration of numerous micromeres, transformed in dense, pycnotic nuclei was observed. It results in an evident decrease in the number of oncospheral cells, from about 70 observed in the early preoncospheral stage to about 26 remaining in the infective oncospheres. The mature oncosphere of A. dentata consists of three pairs of oncospheral hooks, an extensive peripheral, somatic musculature interconnected with a complex system of hook muscles and five cell types: nerve cells, syncytial penetration gland, oncospheral tegument complex, as well as small somatic and large germinative cells. The approximate number of oncospheral cells in A. dentata is 26 and number of oncospheral nuclei is 28. This number includes two syncytial structures, a bi-nucleate tegumental perikaryon and a bi-nucleate penetration gland, as well as about 17 somatic cells which represent perikarya of somatic and hook musculature, 2 nerve cells and 6 germinative cells. The results of this study provide supplementary information and support our hypothesis that the progressive reduction in the number of oncospheral cells is a general trend in cestode evolution (Swiderski 1983) and may represent one of their ontogenetic adaptations.

KEY WORDS: Anoplocephaloides dentata, Anoplocephalidae, Cestoda, embryonic development, ultrastructure, oncosphere differentiation, cellular organisation
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