The critical-point-dried specimens of Gastrothylax crumenifer (Creplin, 1847) Poirier, 1883 and Paramphistomum epiclitum Fischoeder, 1904, both recovered from the rumen of sheep, were studied by scanning electron microscopy at magnifications ranging from 10 to 10,000 x to reveal the structural differences of the tegument between the two species.
In G. crumenifer, both dorsal and ventral surfaces have tubercle-like tegumental elevations, devoid of spines. A row of prominent, regularly arranged, button-like protuberances encircle the rim of mouth. It is suggested that these are sensory in nature. The lining of the buccal tube also bears papillae, some of which appear balloon-like. The tegument near the outer acetabular rim is thrown into prominent ridges bearing groups of six to eight small papilla-like elevations. Towards the interior of the acetabular cavity this pattern merges into one with stout, finger-like projections with groups of papillae at their blunt tips. From their structure, these projections appear to aid strong anchorage to the host's surface and the papillae to be secretory.
P. epiclitum has a similar tuberculated pattern on the dorsal and ventral surfaces. In the oral region, the tegument has some irregular, patch-like elevated areas. The acetabular surface is thrown into a pattern of deep folds and craters.