Uptake and incorporation of [3H]glycine from 1 ?M solutions was observed in the tissues of larval oysters,
Crassostrea gigas, Ostrea edulis, and mussels, Mytilus edulis. In all cases, radiolabel first appears in the larva's velum. Following increasing exposure time, label begins to appear in other organs. In newly settled larvae of the oyster, C. gigas, and the scallop, Pecten maximus, uptake occurs via the developing gill buds. All experiments provide evidence of direct epidermal uptake of soluble nutrients without any participation of the digestive tract. Scanning electron micrographs show that there is no bacterial population visible on the surface of the velum that might act as an intermediate step in nutrient transport. These studies on veligers, pediveligers and settled larvae link the phenomenon of larval uptake with the extensive literature on the direct uptake of soluble nutrients by adult bivalves.