The development of the central nervous system in Capitella capitata (Polychaeta, Annelida)

Abstract

The development of the central nervous system of the polychaete Capitella capitata is described in a series of five stages, using both light and electron microscopy. The initial cerebral primordium is paired and differentiates into two cell types, one electron lucent and granular, the other electron dense. The onset of muscular activity precedes the initiation of axonal growth. Neural differentiation appears to progress anteroposteriorly. Earliest morphological indications of neuromuscular contact are found in the metatrochophore stage. Classically differentiated synaptic junctions were not seen, even in the final settling stage. Development in C. capitata is essentially direct; there are very few larval features and none of these concern the emerging nervous system.