Abstract A controlled laboratory experiment showed that the survivorship of the larvae of Nereis vexillosa Grube is significantly lowered by the feeding activities of Eupolymnia heterobranchia (Johnson). Ingestion of larvae by Eupolymnia is suggested as the mechanism of this interaction. E. heterobranchia eats small metazoans in the laboratory and also has microcrustacean and polychaete hard parts in its feces. These findings support the hypothesis that adult-larval interactions are important in structuring dense marine infaunal assemblages. It is argued that such interactions are important in other types of communities, e.g., terrestial forest and marine fouling communities, when they are at or near their resource limitation.