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

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