Monthly samples of the bivalves Atactodea striata, Gafrariurn turnidum and Anadara scapha were collected over 1 year from the littoral zone on the south-western coast of New Caledonia. A. striata and G. turnidum were studied by macroscopic examination of gonads and microscopic examination of gamete smears. For A. scapha, only microscopic examination was used. A. striata and G. turnidum are dioecious, whereas A. scapha is a protandric hermaphrodite. Sexual differentiation begins at a shell length of 20 mm for A. striata and G. turnidum and 22 mm for A. scapha. The three species have an extended or continuous breeding period, although, in all three, sexual activity peaks in the hot season.