Comparative Analysis of Embryonic Inversion in Algae of the Genus Volvox (Volvocales, Chlorophyta)

Recent literary data on inversion (turning inside out) in the embryos of flagellated algae of the genus Volvox are critically analyzed. In this process, active changes in the shape of embryonic cells and the displacement of intercellular cytoplasmic bridges play an important role. After inversion, the flagella appear on the outer side of the young colony and provide its motility. Within the genus Volvox, two main modes of embryo inversion have been recently established during the asexual developmental cycle—inversion of type A and inversion of type B—represented by the two species most thoroughly studied, respectively, Volvox carterif. nagariensis and V. globator. However, the published opinion that the inversion of V. aureus embryos is of the type B seems to be doubtful. Comparative and evolutionary aspects of embryonic inversion in Volvox are discussed with the use of data on other genera of colonial volvocine algae.