Abstract <p>The methodology of “phylogenetic systematics” in any modern variant, is not based on real biological processes. On the contrary, the construction of models of ancestral ontogenetic cycles is not a hypothetic process but is based on real properties of ontogeny. Models of ancestral ontogenetic cycles and sequences of phylotypic periods in the orders Doridida and Nudibranchia are presented, and for both groups ordinal status is confirmed. It is shown that the current paradigm in the field of reconstruction of the evolutionary history of Bilateria is mobile- and larva-centered, ignoring significant contradictions. A sedentary-pelagic model of the ancestral ontogenetic cycle of Bilateria is presented and shown to be consistent with the current body of evidence.</p>