1974년부터 1975년 말까지 부안만 대합에 기생하는 흡충류 유충의 발육, 기생율, 조직변화 및 사육실험을 통하여 대합의 폐사원인을 밝혔다. 1. 대합의 생식소, 중장선, 새엽에 기생하는 유모 cercaria인 Cercaria pectinata Huet와 그 sporocyst를 검출하였다. 2. 기생충의 수와 량이 급히 증가하므로 흡충류에 기생된 대합은 기능장해를 받아 폐사된다. 3. 부안산 대합 2,639개체에 대한 대합에 기생되는 흡충의 평균 기생율은 $13.2\%$였는데, 월별로 보면 7월이 가장 높았으며$(29.6\%)$, 3월이 가장 낮았다$(2.0\%)$. 한편 각장에 관계없이 기생율은 거의 같았다. 4. 흡충류에 기생된 대합의 생식소는 거세되고, 유충의 증식으로 중장선은 압박을 받으며 새판내에 기생되므로 혈액순환장해를 일으킨다. 5. 수조 내에서 사육한 기생패는 35일만에 전부 폐사했다.
Larval morphogenesis and infection rates of Cercaria pectinata Huet were investigated in regards to histological changes and mortality of the hard clam, Meretrix lusoria $(Rddot{o}ding)$, in Buan located on the Western Coast of Korea. The trichocerous cercariae, Cercaria pectinata, and its sporocysts parasitize mainly in the tissues of goand, digestive gland and gills of the hard clams. One branched sporocyst grows into a great number of cylindrical sporocysts, and a heavily infected clam possesses 2,000 to 5,000 cylindrical spo ro cysts. Each of them produces approximately 30 to 70 germinal cells and cercariae. Of 2,639 clams examined 347 individuals $(13.2\%)$ were found to be infected. The infection rates showed seasonal variations, the rate being highest $(29.6\%)$ in July, and lowest $(2.0\%)$ in March. Whereas, the infection rates did not change significantly with the changes of size class of the shell. No infection was observed in Meretrix petachialis (Lamarck) collected from Myeong-ji, Kimhae Gun located near Busan. In the iefected clams, the gametogenesis (oogenesis and apermatogenesis) did not undergo completely, therefore the heavily infected clam seemed to be castrated. Also the tissues of the digestive gland and gills were compressed by the multiplication of the parasites. When they were kept in aquariums in the laboratory, high mortality has occurred in the infected clams. All of the 60 infected clams died within 35 days.
