Most nereid polychaetes are strictly semelparous, a single episode of reproduction being invariably followed by death. Endocrine manipulation in Nereis diversicolor by the regular implantation of cerebral ganglia from immature donors unveils characteristics associated with a capacity to engage in repeated gametogenic cycling. Such manipulation permits full maturation of the gametes but blocks spawning. Gamete resorption then leads on to another bout of gametogenesis and a new cohort of gametes is formed. The neurosecretory system adopts a cyclical pattern of activity, which parallels that of gametogenesis. Repair and maintenance of the soma continue throughout sexual maturation, as shown by the persistence of feeding and the capacity for regenerative segment proliferation. In consequence, life is extended apparently indefinitely. These latent capacities are reminiscent of features of iteroparous life histories, characterized by repeated breeding, and are postulated to be vestiges of an iteroparous ancestry. They also constitute a preadaptation for iteroparity and reveal how readily a reversal to this condition could occur. The study suggests that reproductive strategies may be unexpectedly labile in even their most fundamental aspects.