The system of multicellular animals presented here is an alternative to the traditional classification system which still operates with the categories of Carl Linné, including typological divisions in artificial species groups. In a new approach to the phylogenetic order in nature this book strives for an objective systematization of the metazoa. It seeks a new path in the field of academic research and teaching based on the theory and methodology of phylogenetic systematics. This volume covers the metazoa from the Porifera up to the Cestoda, Nemertini and Trochozoa; two more volumes to come will cover all the remaining metazoa.