Evolution and development of polarized germ cell cysts: New insights from a polychaete worm, Ophryotrocha labronica

► Oocyte/nurse cell pairs in O. labronica arise by fragmentation of “parental” cysts. ► Parental cysts exhibit indeterminate growth and variable architecture. ► Cystocytes' fate is specified by position in parental cysts, and stochastic events. ► Oogenic cysts exhibit greater evolutionary plasticity than is often appreciated.