Elements of evolutionarily initial morphogenesis providing for the formation of main body axes could have been preserved in embryogenesis of lower Metazoa animals, Cnidaria. However, the information on the morphological bases of axes formation in their normal development is not yet complete. When studying the normal development of Dynamena pumila (Hydrozoa, Thecaphora, Sertulariidae), it has been proposed that the region, where the embryonic ectoblast remained unclosed for the longest time, determines the position of the posterior pole of the larval anteroposterior axis. In the experiments, the formation of closed ectoblast in an arbitrarily chosen region of the embryonic surface was delayed artificially, for example, by incisions. The fate of this region was traced with the help of a mark consisting of carmine particles. It was shown that the posterior pole did differentiate near the region of surface, which was the last to epithelize and redetermination of the anteroposterior axis orientation was only possible before the formation of closed ectoblast in the normal development. The morphogeneses involved in the formation of anteroposterior axis and its poles in Dynamena embryos were reconstructed by means of observations over the displacement of mark particles. It was shown that the establishment of this axis and appearance of morphological differences between the anterior and posterior planula poles are morphogenetic consequences of the closed ectoblast formation. The region, in which the closure of ectoblast is delayed, is a functional analog of the blastopore of higher Metazoa.
Russian Journal of Developmental Biology – Springer Journals
Published: Oct 7, 2004
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