Multiple, alternative cleavage patterns precede uniform larval morphology during normal development of Dreissena polymorpha (Mollusca, Lamellibranchia)

In this study we reinvestigate the early development of the freshwater mussel Dreissena polymorpha, previously studied by Meisenheimer (1901). The data include video time-lapse recordings of living embryos and bisbenzimide stains of fixed embryos as well as morphometry on fixed, serially-sectioned embryos. We present the cell lineage and cell cycle durations up to the first indication of symmetrization within this embryo. We show that early cell cycles last approximately 1h. A dramatic extension of cell cycle duration and a concomitant asynchrony among the various cell lines was observed starting at the fifth cleavage. Short cell cycles, like those of early blastomeres, were a constant prop…