In the course of a DAAD funded research stay of Dr. Christiane Todt (University of Bergen, Norway) the development of excretory organs of a “worm mollusc” (Solenogastres) was investigated at the ZSM. These exclusively marine animals are believed to represent the most primitive molluscs and thus they might exhibit archetypical features during development. As has been suspected earlier by the research group B. Ruthensteiner/G. Haszprunar/N. Baeumler (in the course of a DFG-project currently comparing the development of excretory systems of several molluscan clades), there are two pairs of protonephridia appearing successively during larval development, with the posterior one possibly involved in formation of the adult renopericardial system. These new findings differ fundamentally from what was previously assumed and they shed a new light on mollusk evolution.