The jointed appendage is a key novelty in arthropod evolution and arthropod legs are known to vary enormously in relation to function. Among centipedes, the ultimate legs always are distinctly different from locomotory legs, and different centipede taxa evolved different structural and functional modifications. In Geophilomorpha (soil centipedes), ultimate legs do not participate in locomotion and were interpret to serve a sensory function. They can be sexually dimorphic and in some species, male ultimate legs notably appear “hairy”. It can be assumed that the high abundance of sensilla indicates a pronounced sensory function. This study seeks for assessing the sensory diversity, however, documents the surprising and unique case of an extensive glandular epithelium in the ultimate legs of three phylogenetically distant species. The tightly aggregated epidermal glands with stalked ducts – mistakenly thought to be sensilla – were scrutinized using a multimodal microscopic approach comprising histology as well as scanning and transmission electron microscopy in Haplophilus subterraneus. Hence, this is the first detailed account on centipede ultimate legs demonstrating an evolutionary transformation into a “secretory leg”. Additionally, we investigated sensory structures as well as anatomical features using microCT analysis. Contrary to its nomination as a tarsus, tarsus 1 possesses intrinsic musculature, which is an indication that this podomere might be a derivate of the tibia. The presence and identity of ultimate leg associated epidermal glands with stalked ducts is a new discovery for myriapods. A pronounced secretory as well as moderate sensory function in Haplophilus subterraneus can be concluded. The set of characters will improve future taxonomic studies, to test the hypotheses whether the presence of these specialized glands is a common feature in Geophilomorpha, and that tarsus 1 may be a derivate of the tibia. As the number of epidermal glands with stalked ducts is sexually dimorphic, their function might be connected to reproduction or a sex-specific defensive role. Our results, in particular the unexpected discovery of ‘glandular hairs’, may account for a striking example for how deceptive morphological descriptions of epidermal organs may be, if based on non-invasive techniques alone.

中文翻译：

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当扫描电镜成为一种欺骗性的分析工具时：在地蜈蚣的最终腿上意外发现带有柄管的表皮腺


有关节的附肢是节肢动物进化中的一个关键新事物，众所周知，节肢动物的腿在功能方面存在巨大差异。在蜈蚣中，最终的腿总是与运动腿明显不同，不同的蜈蚣类群进化出了不同的结构和功能修饰。在Geophilomorpha（土壤蜈蚣）中，末足不参与运动，被解释为具有感觉功能。它们可能是性别二态性的，在某些物种中，雄性的终极腿尤其显得“毛茸茸的”。可以假设，高丰度的感器表明明显的感觉功能。这项研究旨在评估感觉多样性，然而，记录了三个系统发育遥远物种的最终腿中广泛的腺上皮的令人惊讶和独特的情况。使用包括组织学以及扫描和透射电子显微镜在内的多模态显微方法对 Haplophilus subterraneus 中紧密聚集的带有柄管的表皮腺（被错误地认为是感器）进行了检查。因此，这是对蜈蚣终极腿的首次详细描述，展示了向“分泌腿”的进化转变。此外，我们还使用 microCT 分析研究了感觉结构和解剖特征。与跗骨的命名相反，跗骨 1 具有内在的肌肉组织，这表明该足节可能是胫骨的衍生物。终极腿相关表皮腺和有柄导管的存在和身份是多足动物的一个新发现。可以得出结论，Haplophilus subterraneus 具有明显的分泌功能和中等的感觉功能。 这组特征将改善未来的分类学研究，以检验这些特殊腺体的存在是否是地螟纲的共同特征以及跗节 1 可能是胫骨的衍生物的假设。由于带有柄管的表皮腺的数量是两性异形的，因此它们的功能可能与生殖或性别特异性的防御作用有关。我们的结果，特别是“腺毛”的意外发现，可能是一个引人注目的例子，说明如果仅基于非侵入性技术，表皮器官的形态学描述可能是多么具有欺骗性。