Ph.D. Thesis

Nephrogenesis in molluscs and sipunculans - did the molluscan kidney evolve independently?

The homology of the molluscan kidneys to (in particular annelid) metanephridia versus a molluscan-specific organ ("emunctorium") is still a matter of debate. Previous studies on nephrogenesis in molluscs are scarce or have been non-conclusive, whereas detailed comparative data on polychaetes are available. Preliminary investigations on nephrogenesis on certain conchiferan molluscs revealed a functional "protonephridial" stage prior to formation of pericardium and heart. This contradicts earlier data on molluscan kidneys being derived from outgrowing "pericardioducts".

The proposed investigation of members of four molluscan "classes" (Polyplacophora, Gastropoda, Bivalvia, Scaphopoda) plus a member of the Sipuncula as outgroup, with a combined light and electron microscopic analysis followed by computer based 3D-visualization shall provide detailed knowledge on nephrogenesis in these taxa. The expected results will provide decisive information on several unresolved issues like: (1) the appearance of a "protonephridial" stage in the basic development pattern of the molluscan adult kidney; (2) the homology relation between the two excretory systems appearing consecutively during ontogeny of molluscs, the protonephridia and kidneys; (3) homology relations of the molluscan and polychaete (and other lophotrochozoan) nephridial systems.