Ultrastructure of the tegumental microvilli (microtriches) of Hymenolepis diminuta

Summary The ultrastructure of microtriches of the rat tapeworm, Hymenolepis diminuta, was examined with a number of electron-microscopic techniques. Fixatives containing different buffers, non-ionic detergents, chelators, tannic acid and various concentrations of aldehydes were tested for ability to stabilize cytoskeletal components while extracting background material. These methods revealed features unique to these specialized microvilli, and permitted construction of a detailed model of microthrix architecture. The microtriches of H. diminuta are comprised of a microfilament-containing base, a dense cap and a complex junctional region between the base and cap. The microfilaments of the base are contiguous distally with a tubular structure (the junctional tubule) within the junctional region; proximally, the microfilaments end abruptly: a terminal web appears to be absent. A beveled bilayered cylinder of dense material (the core tunic) encircles the microfilamentous core. The core tunics and junctional tubules of the microtriches are specifically and uniformly aligned along the strobila. Microtriches therefore can be distinguished from other microvilli (e.g., those of enterocyte brush borders) by their complex ultrastructure and precise orientation upon the cytoplasmic surface.