Cercaria yamagutii Ito, 1957 (C. yamagutii) was found in Lunatia fortuni (L. fortuni) and Neverita didyma (N. didyma) collected from the tideland of Sim-po located at the estuary of the Mankyong River, Chonbuk. It was finally confirmed that the parasite is Acanthoparyphium tyosenense Yamaguti, 1939 (A. tyosenense) and its life history was clarified in this study. Mactra veneriformis (M. veneriformis) was artificially infected with C. yamagutii isolated from L. fortuni and N. didyma. It began to intrude into M. veneriformis through the inhalent canal. Five hours after infection, the tails of the cercaria began to be separated from the main body and the cercaria started to form cysts. Mature cysts were formed 340 hours (14 days) after infection. The cysts were $300sim360{mu}m$ in diameter and the encysted metacercarias were $790sim800 imes300sim310{mu}m$ in size. The metacercarias were administered orally to Larus crassiostris (L. crassiostris), and adult worms of $84.5sim112.5 imes55sim65{mu}m$ were found full of eggs with $2.20~3.70$ mm long and $0.40~0.59$ mm wide after 10 days. In a field study, it was observed that the infection rate of A. tyosenense is $99.5\%$ in M. venerifomis, $76.3\%$ Solen strictus (S. strictus), and $37\%$ Ruditapes philippinarum (R. philippinarum), No difference was found among different host sizes, It was concluded that the first intermediate hosts of A. tyosenense Yamaguti were L. fortuni, N. didyma, Tympanotonus microptera, Cerithidea (Cerithidea) largillierti, Cerithidea (Cerideopsilloa) cingulata, the second intermediate hosts M. venerifomis, S. strictus and R. philippinamn, and the final hosts L. crassiostris and Melanitta fusca stejnegeri.