Differentiation of the Oral–Aboral Axis and Body Parts during Life Cycle Transitions in Scyphozoa

Abstract

Abstract—Differentiation of body axes during formation of primary body plan is one of the most fundamental processes in metazoan development. How did body axes emerge in the course of animal evolution? How did developmental processes associated with axes differentiation evolve? The basal metazoans, representatives of the phylum Cnidaria, are valuable objects for resolving these questions, since they have an evolutionarily simple body plan and only one (oral-aboral) body axis. The high abundance and diversity of the modes of asexual reproduction is an interesting feature of this group. In this review, we summarized the data on the establishment of primary body axis and differentiation of main morphological structures during asexual reproduction in representatives of the class Scyphozoa. We found that the relative orientation of the parental and offspring body axes varies significantly and depends on the mode of asexual reproduction, and that the same body parts of the offspring polyp or medusa can be formed from different parts of the parental organism. The high plasticity of scyphozoan developmental processes can be explained by assuming that various types of asexual reproduction evolved from regeneration processes in this group. To test this assumption, it is necessary to study the molecular mechanisms of differentiation of the primary body axis and the body parts during regeneration and asexual reproduction of scyphozoans.