LARVAL DEVELOPMENT OF A SPIONID POLYCHAETE PARAPRIONOSPIO PINNATA (EHLERS)

Abstract

Data concerning the development of the spionid polychaete Paraprionospio pinnata are derived from specimens which were obtained from the plankton in Kumihama Bay and reared in the laboratory. Descriptions and figures are given on the pelagic larva from 2- to 38-segment stage and the metamorphosed juvenile. The red pigments on the lateral lips and the absence of larval setae in segment 2 are diagnostic features of the larval stage in this species. The characteristics similar to those for the adult (e.g. branchiae, palpi, parapodial lamellae and hooded hooks) appear successively as the larva grows. Metamorphosis occurred at 33- to 37-segment stage in the laboratory culture, of which sizes of the specimens were rather smaller than those of the specimens obtained from the bottom of the sea. Among the spionid larvae listed from the literatures, Paraprwnospio pinnata is largest in size and in the number of segments at metamorphosis.