CENTROCESTUS FORMOSANUS - SURFACE-MORPHOLOGY OF METACERCARIA, ADULT AND EGG

The surface morphology of metacercariae isolated from Puntius spp., ad ult worms from infected hamsters and eggs of Centrocestus formosanus ( Digenea: Heterophyidae) were studied using scanning electron microscop y. It was found that the surfaces of the metacercariae and adult worms were closely similar in appearance. The oral sucker was surrounded by a circumoral expansion with two rows of 32 spines (16 spines each). T he ventral sucker, with six large nonciliated papillae on the lip, and the genital opening were located mid-ventrally. The excretory pore wa s terminal. The body surface was covered with pectinate scale-like spi nes of varying sizes. The scales in the middle area were larger than t hose in the anterior and posterior parts of the body. Sensory papillae , mostly uniciliated, were present in greater abundance at the anterio r region of both stages. However, morphological variations were observ ed among the adults depending on the age of the worms. At 4 weeks, the oral sucker and circumoral expansion were cobblestone-like in structu re and the grooves of spines split compared with their smooth surfaces at 10 days. In addition, the ventral sucker became depressed and its large papillae on the lip disappeared at 10 weeks post infection. Mult iciliated papillae were also present in 10-week old worms. Each egg of this parasite possessed a prominent operculum and a latticed design o n the egg shell.