Nurse egg origin in the polychaete<i>Boccardia proboscidea</i>(Spionidae)

Abstract

Summary Nurse eggs are commonly produced by spionid polychaetes and gastropod molluscs and serve as sources of extra-embryonic nutrition for developing young. Although the influence of nurse eggs on offspring development has been well documented, the origin of nurse eggs is not understood. We examined nurse egg production in the spionid Boccardia proboscidea using brightfield and fluorescence microscopy. Nurse eggs in this species appear to arise as do viable oocytes. After spawning, nurse eggs produce fertilization envelopes indicating that development has been activated. Nurse eggs are also capable of producing polar bodies, which indicates completion of meiosis in those eggs. After activation, nurse egg cytoplasm becomes compartmentalized into small bodies that are ingested by developing larvae and nuclear DNA is lost—processes similar to those observed in apoptotic cells. Thus, nurse egg production in B. proboscidea is an active developmental process and not simply an artifact of sperm limitation.