The
tegumental surface of the newly excysted juvenile, first-week and adult
stages of a human liver fluke, Opisthorchis viverrini, was studied by scanning
electron microscopy. The surface of the newly excysted juvenile is characterized
by circumferentially arranged ridges alternated with troughs which bear
rows of spines encircling the body. These spines are characterized by the
shapes of their edges: the first type with serrated edge appears on the
anterior part, and the second type with single sharp edge appears on the
middle part. There are no spines on the posterior part of the body. Three
types of presumed sensory papillae are present: type A is a single small
cone-shaped ciliated papilla; type B is a group of ciliated papillae on
a common dome-shaped base; and type C is a large papilla with nonciliated
bulb. Type A papillae are scattered evenly on the surface but are more concentrated
around the oral and ventral suckers, as well as the excretory pore. Pairs
of both type A and B papillae are located in rows along the lateral surfaces
of the body. Type C papillae are located solely on the lip of the ventral
sucker. In the first-week fluke the tegumental surface appears corrugated
and covered with short developing microvilli, and spines are mostly lost.
In the fully-grown adult fluke the surface appears highly corrugated with
wave-like folds encircling the body which are covered in turn with closely
packed stubby microvilli. Microvilli are more numerous and are taller on
the ventral than on the dorsal surface. Among microvilli on the surface
of both older stages three types of sensory papillae as in the newly excysted
juvenile were observed, but they are of larger sizes. The number of type
A papilla increases whereas that of type B papilla decreases during maturation.
The distribution of papillae in both stages is similar to the newly excysted
stage.