Time-lapse image acquisition, E. costatus dividing in a microfluidic device. Laser scanning confocal microscopy was used to acquire chloroplast fluorescence. Chloroplast morphology was used as a proxy for cell shape and location. In this acquisition, the bottom-most cell of the eight-cell coenobium exhibited cell mass rotation within the mother cell wall (described in Fig. 3). Four daughters emerge from the top cell as evidenced by unfolding of the coenobium at later time points (490-510 min, described in Fig. S1). The bottom cell also releases a four cell coenobium between 650 and 660 min, which is observed at the very edge of the field of view. The released coenobium eventually drifts away.