Tegumental topography of the plerocercoid of Gymnorhynchus gigas (Cestoda : Trypanorhyncha)

The tegumental topography of the plerocercoid of Gymnorhynchus gigas is des cribed for the first time. The surface features were examined by scanning e lectron microscopy. Eight different types of microthrix pattern were found. Differences in the shape and density of microtriches depend on their locat ion. A unique morphological feature is reported herein, namely, filamentous microtriches that were arranged in clusters with a dome-shaped pattern whe n the bothridial surface was relaxed but sunk into a crater when the bothri dial surface was contracted. In contrast to other trypanorhynchan cestodes, palmate microtriches are not found on the tegument of this plerocercoid. T he microtriches on the caudal extension gradually increased in length with growing distance from the blastocyst, which showed short knob-like structur es. These structures developed into elongated filiform microtriches on the posterior region of the caudal extension.