Evolutionary Conservation and Variability of the Mesoderm Development in Spiralia: A Peculiar Pattern of Nereid Polychaetes

An analysis of the comparative-morphological, molecular-genetic, and evolutionary aspects of the teloblastic mesoderm formation in the Spiralia representatives was performed. The conservative and the most expressive varying features of morphogenesis and genetic developmental programs of the mesodermal germ layer were considered. Using nereid polychaetes, we revealed peculiarities of their developmental patterns, related to the role of inductive interactions and the dynamics of the molecular profile in the formation of mesodermal derivatives.