A number of studies on the papillae of cercariae of trematodes reported that the papillar patterns (or chaetotaxy) of cercariae might be an excellent method to attain better understanding of the digenetic trematodes (Richard, 1971; Short and Cartrett, 1973; Bayssade-Dufour, 1979). The present study was aimed to determine the number, distribution pattern and structure of the sensory papillae of Metagonimus yokogawai cercariae, and to elucidate the chaetotaxy of this digenetic trematode. M. yokogawai cercariae were pipetted from a vial in which infected snails (Semisulcospira libertica) had been kept for 3 hours. The snails were collected from an endemic area of M. yokogawai, Boseong river in west-southern part of Korea. Observations of papillae were based on light microscopy of those stained with silver nitrate, and on scanning electron microscopy. The results are summarized as follows: All papillae observed were uniciliated. Cilia in anterior tip were shorter than the others in other portions. The body papillae were arranged in essentially symmetrical patterns. Total number of the papillae was 126(63 pairs) in average; anterior tip 40(20 pairs), ventral 20(10 pairs), lateral 42(21 pairs), and caudal 8(4 pairs). The chaetotaxy of M. yokogawai cercaria was; C(I) cycle (3+3C(I)V, 2+2C(I)L, 2+3C(I)D), C(II) cycle(2C(II)V, 1C(II)L, 2C(II)D), C(III) cycle (1+lC(III)V, 1C(III)L), C(IV) cycle (1C(IV)V, 1C(IV)L) in cephalic region: A(I)(lA(I)V, l+2A(I)L, 1A(I)D), A(II)(1A(II)V, 1+3A(II)L, lA(II)D), A(III) {lA(III)V, l+lA(III)L, lA(III)D) and A(IV)(lA(IV)V, 2A(IV)L) in antacetabular region: 1M(I)V and 2M(I)L in median: 1+lP(I)L, 1P(II)L, lP(II)D lP(III)L, lP(IV)L and 1P(IV)D in postacetabular region: 2-2-2-2 in caudal region.
