Notes on the morphological changes in the oocyte of the polychaete Perinereis wilsoni (Glasby and Hsieh 2006) from spawning to the early larval stage

ABSTRACT Perinereis wilsoni is a nereidid polychaete species with segments that are completely separated from each other by a septum. Recent molecular studies on this species discussed the mechanism of male and female germ cell development and germ cell regeneration. Although several molecular studies have been conducted on this species, its embryonic and larval development have not yet been described. To address this, oocyte development from spawning to the early juvenile stage was monitored. Morphological changes in relation to minutes/hours post-fertilization are described. We found several changes in the oocyte egg envelope before the start of cell division. During embryonic development, the larvae left the jelly layer as a 3-segmented nectochaete possessing a complete adult body plan, typical of the direct larval development in this species. The dorsal pygidial cirri were observed to develop fully during the five-segmented nectochaete stage. This paper provides important information on an aspect of the reproductive biology of this species.