We report for the first time annual gametogenesis in the Chinese anapella clam Coecella chinensis (Deshayes 1855) living on an upper intertidal sandy beach on the eastern coast of Jeju, Korea. Using histological methods, gonadal maturation, oocyte area in the follicle (follicle index, FI), and oocyte diameter were investigated. Gametogenesis began in the middle of April, when the sediment temperature was 13°C. Annual maximum oocyte size and FI peaked in July, when water temperature reached 20°C and sediment temperature reached 35°C. Subsequent spawning of C. chinensis occurred in August and continued until the end of September. Mean ripe oocyte diameter was 31.2 μm, which is comparatively smaller than that of other bivalves. Clams over 15.7 mm in shell length had mature gonads, indicating that this size is a biological minimum for reproduction. Annual sediment temperature fluctuation was positively correlated with condition and gonadal development (P < 0.01), indicating that cyclic changes in gametogenesis are in part governed by substrate temperature. The relatively smaller eggs observed here are believed to be a reproductive strategy of C. chinensis, an adaptive trade-off between reproduction and growth in the food-poor upper intertidal environment.