Phylogenetic Exercises with Monophyletic Groups of Sponges

The classification of the Porifera is critically evaluated using cladistic principles. The (syn-)apomorphic characters and character states are established for 34 groups of Porifera which are generally accepted as monophyletic. These characters/states are compared with the currently accepted classification of Hartman (1982), resulting in the conclusion that there are many non-parsimonious homoplasies included. Two consecutive attempts to amend this are presented. The first consists of a self-constructed strictly cladistic classification characterized by the assumption of many assumed losses. The second is a computer-based analysis characterized by a neutral construction of a classification with the least number of assumed homoplasies.