Littorina melanostoma, living high in the tidal range on mangrove vegetation, has reproductive systems similar to those of other littorinids but characterized especially by a closed, tubular prostate and simple penis in the male, and by complex, spiral pallial glands in the female. Eggs are released in simple pelagic capsules which hatch to release veliger larvae in seven days. Egg capsules are released almost entirely during the periods of spring tide associated with full moon. Such release occurs at all seasons of the year. Some females release eggs at successive full moons but it appears likely that many females more commonly release eggs at alternate full moons. There is no evidence of endogenous rhythms of egg release related to the times of high tide or the day/night cycle.