FROM "TREE-THINKING" TO "CYCLE-THINKING": ONTOGENETIC SYSTEMATICS OF NUDIBRANCH MOLLUSCS

During the last decade traditional morphological paradigm of evolutionary biology has been challenged. Molecular systematics and morphology-based phylogenetics were considered as "advanced" fields compared to the "old-fashioned" traditional systematics. At the same time, an enormous body of the practical and theoretical methods of "traditional" biology was considered usually in a minimal degree. It is here demonstrated that the current evolutionary paradigm in the "phylogenetic era" lacks a theory of how organisms change their shape. The links between evolution, ontogeny, systematics and phylogenetics are prima facie obvious, but similarly greatly underestimated currently, though the field of "evo-devo" is continuously growing. As a synthesis (or more exactly, re-synthesis) of the still in considerable degree independently developing major biological fields, i.e. ontogeny, evolution and taxonomy, the new conception of onto genetic systematics is therefore suggested; the practical usefulness of the new concept is illustrated by some examples from nudibranch molluscs. Such re-formulation of apparently well-known and obvious biological knowledge implies also a great challenge for current phylogenetics and systematics: an understanding of the necessity to consider not only evolutionary "lines" and "branches" of the "Tree of Life", but also its cycle nature, since ontogenetic cycles are indispensable and active parts of the process of evolution.