OPISTHORCHIS-VIVERRINI - ULTRASTRUCTURE OF THE TEGUMENT OF THE FIRST-WEEK JUVENILES AND ADULT FLUKES

The tegument of one-week-old and adult flukes of Opisthorchis viverrin i were studied by transmission electron microscopy. The tegument of bo th stages is composed of a syncytium formed by processes of the tegume ntal cells lying underneath the outer-circular and the inner-longitudi nal muscle layers. The tegument is bounded by trilaminate outer and in ner membranes; the former is coated with a thin glycocalyx, while the latter has short basal infoldings. There are 4 forms of tegumental gra nules, namely dense spherical, dense discoid, light spherical and ligh t discoid granules. Dense spherical and dense discoid granules have si milar dense homogeneous and highly electron-dense matrices; thus, they may represent different planes of sections of biconcave granules, and may contribute their content to the formation of the outer membrane a nd the glycocalyx. Light spherical and light discoid granules may be a nother type of granule whose filamentous content may contribute to the formation of the microtrabecular network in the tegument. Microvilli start to develop in one-week-old juveniles and become fully developed in adult stages. The size, number and cristae of the mitochondria beco me increasingly more numerous along with the development of microvilli ; in the first-week juveniles most mitochondria are located in the bas al portion of the tegument while in adults most lie within microvilli underneath the outer membrane. The tegumental cell is irregular in sha pe and contains a nucleus with a prominent nucleous, abundant rough en doplasmic reticulum, well developed Golgi complexes, ribosomes, mitoch ondria and numerous tegumental granules. These features indicate that the cell is an active secretory cell, whose product is tegumental gran ules that may be transported via microtubule-lined cytoplasmic process es to the syncytium.