Those who wish for permanence in classifi­ cation must pay the price of stasis - as if for­ ever condemned to confound whales with fish. M. T. Ghiselin 1981, p. 283 Scientific argument is a debate concerned with the solution of unresolved problems. Before continuing with the phylogenetic system of the Metazoa this foreword gives me the opportunity to discuss some controversial ques­ tions, to state selected positions more precisely and to remedy omissions. I would like to draw special attention to serious problems for phylogenetic systematics resulting from the inevitable confrontation with the current rules of nomenclature 1. In carrying out this debate, I hope not to lose the goodwill of those readers who are experts within the first few pages. A textbook for students? - Critics who ask that question and answer in the negative probably underestimate the open-mindedness of young people who are not troubled by, or can easily free themselves from, the restraints and arbitrariness of traditional classifications - and to whom systematics is offered as a scientific product in such a form that arguments for every single decision are comprehensible and checkable and can therefore be fully analyzed.