Paleobiology of the Stem Group Mollusca

目的是对最早的软体动物及其相关无脊椎动物的起源有一个新的认识。寒武纪含片化石动物研究的最新进展为研究原始的毛状软体动物(无足类和壳类)与相关的软体动物门(环节动物、新生纲和管壳纲)之间的关系提供了机会。这些寒武纪化石似乎弥合了活着的门之间的一些形态差距，并暗示了矿物骨骼可能是如何最初在软体动物中进化的。我们打算从活着的刺状软体动物中获得18S rRNA序列，以测试无尾轮虫是最原始的活软体动物还是次级简化的软体动物。此外，我们计划研究聚壳藻板的结晶学，以检验石灰石层间文石不同于甲壳软体动物的层间结构的假设，因此不同于甲壳软体动物的层间结构。同时，我们打算将软体动物针状物的微结构与从寒武纪石灰岩中提取的各种片岩进行比较。这项工作有望为软体动物的早期历史和后生动物的整体进化提供新的见解。

The objective is a new understanding of the origin of the earliest Mollusca and related invertebrates. Recent advances in the study of sclerite-bearing animals from the Cambrian provide an opportunity to investigate the relationship between primitive spiculose molluscs (aplacophorans and chitons) and related soft- bodied phyla (annelids, nemertines, sipunculans). These Cambrian fossils appear to bridge some of the morphological gaps between living phyla and to suggest how mineral skeletons might have first evolved within the Mollusca. We intend to obtain 18S rRNA sequences from living spiculose molluscs in order to test whether aplacophorans are the most primitive living molluscs or are secondarily simplified. Furthermore, we plan to investigate the crystallography of polyplacophoran plates to test the hypothesis that chiton crossed-lamellar aragonite is different from and therefore not homologous to the crossed-lamellar structure of the shelled (conchiferan) molluscs. At the same time we intended to compare the microstructures of molluscan spicules with a variety of sclerites extracted from Cambrian limestones. This work is expected to provide new insights into the early history of the Mollusca and the evolution of the Metazoa as a whole.