Michalski Hanna, Harms Danilo, Runge Jens, Wirkner Christian S
Allgemeine & Spezielle Zoologie, Institut für Biowissenschaften, Universität Rostock, Universitätsplatz 2, 18055, Rostock, Germany.
Zoological Museum Hamburg, Leibniz-Institute for the Analysis of Biodiversity Change (LIB), Martin-Luther-King-Platz 3, 201465 Hamburg, Germany.
Arthropod Struct Dev. 2022 Jul;69:101165. doi: 10.1016/j.asd.2022.101165. Epub 2022 Jun 21.
Pseudoscorpions are an ancient and globally distributed lineage of arachnids with more than 4000 species. Despite being present in virtually all terrestrial habitats, their morphology and anatomy has rarely been studied to date, which hampers homology statements both within and between other arachnid orders. All pseudoscorpions share a morphological peculiarity, the fixation of the coxae of all the walking legs. The same morphological condition is seen in certain other arachnid taxa, such as Solifugae or Scorpiones - potential sistergroups of Pseudoscorpiones. To investigate the musculature apparatus of this unusual feature, we reconstructed the musculature in the coxae of walking legs in three species of pseudoscorpions that represent the three major clades within this order. Using micro-computed tomography (μCT), we show that pseudoscorpions have the highest number of coxal muscles amongst the arachnid orders (12 vs. fewer than 10 in others), and that the muscular composition of the first two legs differs from that in the hind legs, correlating with the difference in function, i.e. pulling in the front legs and pushing in the hind legs. Pseudoscorpions are also unique amongst the arachnids in lacking endoskeletal structures (coxal apodeme or costa coxalis) inside the coxae. We observed that within pseudoscorpions, there is a trend towards a reduction of the number of coxal muscles, with the most basal-branching taxon having the highest number and more derived taxa exhibiting lower counts. We hypothesize the muscular ground pattern for Pseudoscorpiones and discuss the evolution of this system by comparing it to the (scanty) data on other arachnids available in the literature.
伪蝎是蛛形纲动物中一个古老且分布于全球的谱系，有4000多种。尽管几乎存在于所有陆地栖息地，但迄今为止它们的形态学和解剖学很少被研究，这阻碍了在其他蛛形纲目内部以及之间进行同源性描述。所有伪蝎都有一个形态学上的独特之处，即所有步足的基节固定。在某些其他蛛形纲类群中也能看到相同的形态状况，比如避日蛛目或蝎目——伪蝎目的潜在姐妹类群。为了研究这一独特特征的肌肉组织，我们重建了代表该目三个主要分支的三种伪蝎步足基节中的肌肉组织。使用微计算机断层扫描（μCT），我们发现伪蝎在蛛形纲目中基节肌肉数量最多（12块，而其他类群少于10块），并且前两条腿的肌肉组成与后腿不同，这与功能差异相关，即前腿用于拉，后腿用于推。伪蝎在蛛形纲动物中也是独特的，因为它们的基节内部缺乏内骨骼结构（基节内突或基节肋）。我们观察到在伪蝎内部，存在基节肌肉数量减少的趋势，最基部分支的类群基节肌肉数量最多，而更进化的类群数量较少。我们推测了伪蝎目的肌肉基本模式，并通过将其与文献中关于其他蛛形纲动物的（稀少）数据进行比较来讨论这个系统的进化。
