These legs were made for walking... - Evolutionary morphology of the walking appendages in arachnids (Chelicerata; Arthropoda)

蜘蛛类有四对主要用于移动的附肢。从系统发育的角度来看，蜘蛛纲组成了一个单系群，这意味着它们的共同祖先已经拥有这四对运动附肢。然而，当比较最近的分类群中的附属物时，很明显存在着广泛的形态差异，在许多不同的水平上可以观察到结构上的差异。类群内部的变异主要发生在属于不同节段的腿上，以及同源附属物中的类群之间，即属于同一身体节段。关于螯合行走腿的研究有很长的历史，关于同源性，已经探索了许多不同的方法，包括i)关节类型，ii)肌腱附着，以及iii)肌肉插入。然而，以前的大多数研究都集中在足节的数量、关节的排列或它们的肌肉结构上，而对腿的神经支配的研究要少得多。对蜘蛛纲所有这些特征的分析还没有完成。尽管蜘蛛纲运动肢体的使用方式，即行走，在蜘蛛纲进化过程中没有显著变化，但发现了两种不同的腿部伸展方式。虽然一些分类群以液压方式伸展主要关节，但缺乏肌肉，否则就没有这样做的肌肉，而另一些分类群则使用肌肉延伸其主要关节。这两种机制的结构基础都没有得到很好的理解。目前还不清楚所有的蜘蛛纲动物是否以及在哪里有伸腿的肌肉，在液压伸展的情况下，负责产生压力的结构仍然存在一些争论。然而，有一点是明确的，因为液压是在假肢中产生的，所以对蜘蛛腿的比较形态研究也必须考虑到假肢。本研究从三维角度分析了所有主要螯合科的代表(约20种)的原生丝虫和运动附属物的全套。将使用µCT研究外骨骼、肌肉和肌腱的这些特征。将使用免疫标记结合激光扫描共聚焦显微镜来探索腿部的神经支配。在选定的物种中，回填技术将补充这些数据。为了数据交流的目的，所有研究的结构将使用交互式虚拟3D格式结合基于本体结构化词汇的语言描述来记录。在这些描述的基础上，将制定列出的腿部特征同源的组合假设，从而允许详细分析蜘蛛纲动物中行走的腿和生殖器的结构进化，蜘蛛纲动物是最有可能在大约420 Ma前征服陆地的一群海龟。

Arachnids possess four pairs of appendages primarily used for locomotion. From a phylogenetic point of view arachnids constitute a monophyletic group, meaning that their common ancestor already possessed these four pairs of locomotory appendages. Nonetheless, when the appendages are compared in recent taxa, a broad morphological disparity is apparent, with structural differences observable at a number of different levels. Variation within taxa mainly occurs in legs belonging to different segments, and between taxa in homologous appendages, i.e. belonging to the same body segment. The study of chelicerate walking legs has a long history and a number of different approaches have been explored with regard to homologizations, including i) types of joints, ii) attachment of tendons, and iii) insertion of muscles. Most previous studies, however, have focused on either the number of podomeres, the arrangement of joints or their musculature, and much less on the innervation of the legs. An analysis of all these features across Arachnida has yet to be performed.Although the way in which arachnid locomotory limbs are used, i.e. for walking, has not changed significantly during arachnid evolution, two different methods of leg extension are found. While some taxa extend major joints hydraulically and lack the muscles to do so otherwise, others extend their major joints using muscles. The structural basis of neither mechanism is well understood. It is not clear for all arachnid taxa whether and where muscles for leg extension are present, and in the case of hydraulic extension the structures responsible for generating pressure are still the matter of some debate. What is clear, however, is that since hydraulic pressure is generated in the prosoma, comparative morphological studies of arachnid legs must also take the prosoma into account. This study sets out to three-dimensionally analyze the complete set of prosomata and locomotory appendages of representatives of all major chelicerate lineages (~ 20 species). These features will be studied with regard to the exoskeleton, muscles and tendons using µCT. The innervation of legs will be explored using immunolabelling combined with confocal laser-scanning-microscopy. In selected species, backfilling techniques will complement these data. For the purposes of data communication, all studied structures will be documented using interactive virtual 3D formats in combination with linguistic description based on ontologically structured vocabularies.On the basis of these descriptions, combined hypotheses for the homologization of the listed leg features will be formulated, permitting a detailed analysis of the structural evolution of walking legs and prosomata in arachnids, the group of chelicerates that most probably conquered land as early as around 420 Ma ago.