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Acta Parasitologica, Vol.45, No. 2, 2000, 71-82
Swiderski Zdzislaw (1,2), Tkach Vasyl V. (1,3), Vaucher Claude (4), - Fine structure of the infective eggs of the dilepidid cestode Hepatocestus hepaticus (Baer, 1932), a parasite of shrews.

(1) W. Stefanski Institute of Parasitology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland; (2) Department of General Biology and Parasitology, University of Medical Sciences, Chalubinskiego 5, 02-004 Warszawa, Poland; (3) I. I. Shmalghausen Institute of Zoology, Ukrainian National Academy of Sciences, 15 Bogdan Khmelnitsky Str., Kiev-30, MSP, 252601, Ukraine; (4) Natural History Museum, 1 Route de Malagnou, 1211 Geneve 6, Switzerland

Ultrastructural characteristics of the eggs of the dilepidid cestode, Hepatocestus hepaticus, is described. The mature oncosphere is surrounded by three envelopes: (1) an outer envelope; (2) an inner envelope consisting of three layers - an extraembryophoral cytoplasmic layer, a thick, fibrillar, low electron-dense embryophore, and intraembryophoral cytoplasmic layer, (3) a thin oncospheral membrane, surrounding the oncosphere. The whole surface of the oncosphere is covered by the cytoplasmic oncospheral tegument with numerous short microvilli and a layer of subtegumental somatic muscles. The following cell types were distinguished in the mature oncospheres: the U-shaped penetration gland a containing a large amount of tightly packed secretory granules; bi-nucleate perikaryon of the oncospheral tegument; somatic cells (= myocytons of somatic and hook muscles); and the germinative cells. The hook-muscle system consists of three pairs of embryonic hooks and a complex system of specialised muscle fibers responsible for the coordinated hook movements. The ultrastructural characteristics of H. hepaticus oncosphere are discussed in comparison with those of previously studied dilepidids and other cyclophyllideans.

KEY WORDS: egg ultrastructure, oncospheral cell types, oncospheral envelopes, Cestoda, Dilepididae, Hepatocestus hepaticus
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