For the first time, under laboratory conditions, development of the polychaete Namanereis littoralis (Grube, 1876) is investigated. Under conditions of the Sea of Japan, its reproduction occurs in July and is confined to the season of monsoon rains. Fertilization is external. Spawning manifests no epitocous transformations. Fecundity is low, ovicells are rich in yolk, and development is nonpelagic, lecithotrophic, embryonized, characterized by a high rate--5-8 days--and occurs in mucous clutches up to hatching of benthic juveniles. Temperature and salinity optima of development are 22-27 degrees C and 16-21 per thousand, respectively, characterizing the species as subtropical brackish-water by its origin. Archaic and specialized traits are noted in the early ontogenesis of N. littoralis.