Elucidating the phylogeny of the Diplopoda: microCT-scans, morphology and morphometrics of all millipede orders

千足类(双足类)是最古老的陆地多细胞生物之一，所描述的物种有12.000种，是陆地节肢动物的第三大类别。作为有害的食肉动物，它们对分解和土壤形成起着重要的作用。尽管它们的系统发育年龄和它们对了解陆地早期殖民的明显价值，双足类的形态仍然被严重地研究得不够。这对于16个千足目中的稀有代表来说尤其如此，如管足纲、管足目或管足纲。事实上，许多作者抱怨说，我们对双足类的形态知识已经达到了100年前对六足类、甲壳纲和蜘蛛纲的水平。有了这个项目，我们将在一定程度上克服形态知识的不足。利用同步加速器微型计算机断层扫描和组织学的结合，我们手头有工具将千足类的形态知识带到下一个水平。我们的目标是首先为双足纲所有主要类群的48多名代表提供一个数字的、开源的同步微CT扫描和3D模型库，这将涵盖它们的大部分形态和系统发育多样性。其次，我们将利用这种比较的形态信息来为一个有充分根据的系统发育做出贡献。在这个框架内，我们将特别关注形态特征系统，如口器、内骨骼、生殖器结构和气管袋配置。在第三步中，我们将使用几何形态计量学方法来定量研究所选字符系统内的进化形状变异，涉及(A)系统发育信号，(B)进化异速生长和(C)形状变异与各种生态因素的潜在相关性。这将增加我们对形态变化的理解，以响应与千足类相关的特定环境，这将使我们能够重建双足类祖先首次殖民陆地的祖先条件。我们的贡献将提供有关物种丰富的节肢动物群体的关键形态适应信息。

Millipedes (Diplopoda) are among the oldest terrestrial multicellular organisms, and with 12.000 described species the third largest class of land arthropods. As detritivores they play an important role for decomposition and soil formation. Despite their phylogenetic age and their obvious value to understand the early colonization of the land, the diplopodan morphology is severely understudied. This is especially true for the rare representatives among the 16 millipede orders, such as Siphoniulida, Glomeridesmida, or Siphonocryptida. In fact, numerous authors complained that our morphological knowledge of the Diplopoda is at the same level reached for Hexapoda, Crustacea, and Arachnida already 100 years ago. With this project, we will partly overcome this deficit in morphological knowledge. Using a combination of synchrotron micro-computed tomography and histology, we have the tools at hand to take our knowledge of the morphology of millipedes to the next level. Our aim is to first provide a digital, open-source annotated library of synchroton micro-CT scans and 3D-models for more than 48 representatives of all main groups within Diplopoda, which will cover large parts of their morphological and phylogenetic diversity. Secondly, we will use this comparative morphological information to contribute to a well-founded phylogeny. Within this framework, we will especially focus on morphological character systems, such as mouthparts, endoskeleton, genital structures, and tracheal pouch configuration. In a third step, we will use a geometric morphometric approach to quantitatively investigate evolutionary shape variations within the chosen character systems with regards to (a) phylogenetic signal, (b) evolutionary allometry and (c) potential correlation of shape variation with various ecological factors. This will increase our understanding of morphological changes in response to the particular environment relevant for millipedes, which will enable us to reconstruct the ancestral conditions under which ancestors of the Diplopoda first colonized land. Our contribution will provide information about key morphological adaptations for a species-rich group of arthropods.