ИСТИНА

Hydrozoa is the most evolutionary advanced group of the phylum Cnidaria. All colonial hydrozoans grow continuously, changing the shape of their colonies and spreading over the substrate with the help of elongating stolons. Exhibiting high diversity of the colony architecture, they represent ideal objects for comparative and evolutionary morphology. The hydrozoan Dynamena pumila (Linnaeus, 1758) demonstrates higher complexity of the colony structure. The growth of Dynamena colony is accompanied by a variety of morphogenetic processes. Our work is focused on the formation of the anchoring disk (AD) of the stolon. Successive stages of the AD development were described with LM, CLSM and TEM. The AD is formed in the point of the stolon and stem branching, where stolon expands dividing into the several lobes by deepening folds. We have shown that formation of these folds is associated with accumulation of F-actin in the apical domains of the bottle cells located at the bottom of the emerging fold. This may indicate active invagination, although this process has never been described in the development of hydrozoans. We also found the cells with constricted basal domains situated on the sides of the fold. These cells may help to deepen the fold by creating the inverse curvature. Stabilization of the curvature can be provided by the secretion of the chitinous perisarc into the forming fold. Apparently, development of the AD can be viewed as a reliable and versatile model system for studying the cell-shape-change-driven epithelial sheet morphogenesis, which can be easily observed and analyzed.