ИСТИНА

Currently we agree that cnidarians possess bilateral symmetry, at least at the level of genetic regulatory toolkit. However, representatives of corals display morphological six-fold or eight-fold radial symmetry, hydrozoans – radial symmetry, scyphozoans and cubozoans are characterised by the dominance of tetramerous symmetry. For the first time the tetramerous symmetry of scyphozoans becomes apparent at the polyp stage due to the four septa in the gastric cavity. The mechanisms governing the septa development are still unknown. Some time ago, Berking (2007, 2010) proposed the model of septa development regulation in corals and scyphozoans. The main idea is that the lining of the gastric cavity of the developing polyp should be composed of two or three compartments (stripes) with different properties. The border between two different compartments will demarcate the place of septum development. Detailed investigation of the Aurelia aurita larva metamorphosis supports this idea. The endoderm of competent larva consists of three compartments: the vacuolated anterior one, the middle granulated dark one, and the vacuolated posterior one. During metamorphosis, these compartments of endoderm behave differently. The posterior endoderm participates in the development of the first pair of tentacles. The middle endoderm participates in the development of the second pair of tentacles and most of the gastrodermal lining of the polyp calyx. The anterior endoderm transforms into the polyp peduncle gastrodermis. The four septa of the primary polyp develop exactly at the place where the posterior and middle endoderm compartments contact in the circumference of the polyp oral disk between the bases of the primary four tentacles. At these points, the inner manubrium lining (originating from the ectoderm) has direct contacts with the epidermis at the base of the tentacles that can serve as additional signal for septa initiation. The work was supported by RFBR Grant #19-04-01131-a.