This study deals with the reproduction and development of the most common species of peanut worms from the Sea of Japan: Thysanocardia nigra, Themiste pyroides, and Phascolosoma agassizii. Data on the time of reproduction and larval settlement and the distribution of these species in Peter the Great Bay are provided. The peculiarities of gametogenesis, spawning, and embryonic, larval, and postlarval development are described. The reproductive biology of representatives of these species from the western and eastern Pacific is examined in a comparative aspect.