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

软体动物肾脏与(特别是环节动物的)后肾和软体动物特有的器官(“胚囊”)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，或者没有定论，而关于多毛类的详细比较数据是可用的。对某些甲壳纲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，有一个功能正常的原肾期。这与早先关于软体动物肾脏是由不再生长的“心包导管”而来的数据相矛盾。对4个软体动物纲(多足纲、腹足纲、双壳纲、钩足纲)的成员以及作为外群的Sipuncula成员进行的拟议调查，结合光学和电子显微镜分析以及基于计算机的三维可视化，将为这些分类群的肾脏发生提供详细的知识。预期结果将为尚未解决的几个问题提供决定性的信息：(1)软体动物成体肾脏基本发育模式中“原肾”阶段的出现；(2)在软体动物个体发育过程中相继出现的两个排泄系统之间的同源关系；(3)软体动物和多毛类(及其他光游动物)肾系统的同源关系。

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.