Scanning and transmission electron microscopic examinations of tissue-dwelling third-stage larvae of the nematode Cystidicoloides ephemeridarum from the intermediate host (Ephemera danica) were carried out with respect to the morphological changes in the body wall associated with the transfer from the intermediate to the definitive host. The ultrastructure of the cephalic end and zonation of the somatic cuticle of infective larvae basically correspond with those of adults. The somatic cuticle is composed of a fuzzy epicuticle, an outer and inner cortical zone, a median zone and a basal zone consisting of three subzones. Globular bodies are absent from the median zone of the infective larvae. The lateral hypodermal cords of the infective larvae are cellular, consisting of a median cell enclosed by two sublateral cells. The excretory canal is present within each of the lateral cord in both the infective and adult stages. Walls of the excretory canals contain Golgi-derived vesicles which communicate with the lumen of the canal. Large deposits of glycogen, suggesting anaerobic respiration, are present in the hypodermal cords and noncontractile parts of the muscle cells of the third-stage larvae within the intermediate host.

Institute of Parasitology Academy of Sciences of the Czech Republic Branisovská 31 370 05 Ceské Budejovice Czech Republic

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Comparative studies on intestine ultrastructure of third-stage larvae and adults of Cystidicoloides ephemeridarum (Nematoda, Cystidicolidae)