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

软体动物肾脏（特别是环节动物）的后肾与软体动物特异性器官（“腹腔”）的同源性仍然是一个有争议的问题。以前关于软体动物肾脏发生的研究很少或没有结论性，而关于多毛类的详细比较数据是可用的。对某些针叶类软体动物肾脏发生的初步研究表明，在心包和心脏形成之前，有一个功能性的肾原期。这与早期关于软体动物肾脏来源于生长已久的“心包”的数据相矛盾。对四个软体动物纲（Polyplacophora, Gastropoda, Bivalvia, Scaphopoda）的成员以及Sipuncula的成员作为外群进行调查，结合光学和电子显微镜分析以及基于计算机的3d可视化，将提供这些分类群肾脏发生的详细知识。预期的结果将为几个尚未解决的问题提供决定性的信息，如：(1)在软体动物成年肾脏的基本发育模式中出现“肾原”阶段；(2)软体动物个体发育过程中连续出现的两种排泄系统——肾原体和肾脏的同源性关系；(3)软体动物和多毛类（及其他光面动物）肾脏系统的同源关系。

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. Own 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 3Dvisualization 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.