A Study on the fine tegumental structures of the metacercaria and juvenile stages of Clonorchis sinensis

This study was carried out to observe the chronological tegumental changes of juvenile C. sinensis using scanning and transmission electron microscopes (SEM and TEM). The subjected worms were the excysted metacercaria, and l day, 1 week, 2 week and 4 week old worms. By observation with SEM, the tegument of excysted metacercaria showed many transverse wrinkling or shallow rugae, especially remarkable in anterior half of body, i.e., anterior to ventral sucker. Many spines were arrayed on the whole body surface, and double or triple pointed on anterior half and single pointed on posterior half. The observed sensory papillae were composed of 3 types. The ciliated knob-like papillae (type A in Fujino's classification) were abundant on anterior half, especially around oral sucker. A few plate like elevated papillae (type B) were found on middle part and non-ciliated round swellings (type C papillae) were observed around ventral sucker. The tegumental surface of 1 day old worms showed deeper rugae, and the posterior body end was covered with cobble stone-like processes of distal cytoplasm. The spines protruded further and the spines on posterior half of body changed to scale-like ones. The tegument of 1 week old worms became velvety and the spines grew further in length, but the density decreased. The tegumental processes differentiated much finely in the 2 week and 4 week old specimens and the spines or sensory papillae decreased of their relative density. The basic tegumental structures, such as distal cytoplasm containing various granules, vesicles and spines, basement membrane complex, muscular layers and tegumental cells were also monitored in 1 week old worms by TEM.