ON THE REPRODUCTION AND LARVAL DEVELOPMENT OF STREBLOSPIO BENEDICTI WEBSTER,

Abstract

1. The larval development of the larviparous spionid polychaete, Streblospio benedicti, is described. Specimens were obtained from adults maintained in the laboratory and from plankton isolates. Early and late trochophores, 7-, 9- and 11-setiger stages are illustrated. 2. Undisturbed adult females retain larvae until the 9-setiger stage. If stimulated, however, the female will release younger stages. Under laboratory conditions, late trochophores and all later stages can be reared through metamorphosis. Larvae can metamorphose once they acquire 9 setigers, but they can delay metamorphosis until the 13-setiger stage in the absence of a suitable substratum. Rarely will larvae metamorphose in the absence of sediment. Pelagic life is usually three days or less but can be prolonged for at least two weeks. 3. Seven- to 13-setiger S. benedicti larvae occur in the plankton of the Mystic River Estuary from June to October. Nine- and 10-setiger larvae are encountered most frequently.