Comprehensive morphological investigations covering the diversity of metazoan lineages are needed to obtain a complete picture of organ system evolution. Despite the increased amount of studies on lesser-known phyla during the last decades, the gap in knowledge for these lineages is still remarkable. This is the case for kinorhynchs, or mud dragons, where only a few genera, mainly belonging to the major clade Cyclorhagida, have undergone detailed morphological examinations. Here, we explore the neuroanatomy and myoanatomy in the other major clade, Allomalorhagida, through studies of Dracoderes abei and Pycnophyes ilyocryptus by immunochemistry, CLSM, and computational 3D reconstruction. The current phylogenetic position of Dracoderes as a sister group to all the remaining allomalorhagids makes it a key taxon for understanding the evolution of organ systems within Kinorhyncha. Clear segmental arrangement of muscles and nerves was found in the trunk of D. abei and P. ilyocryptus, excluding modifications observed in the posteriormost segments. When comparing current and previous studies of allomalorhagids and cyclorhagids, the nervous system shows a conserved pattern across kinorhynchs, while the musculature shows significant variation among genera. Segmentation in kinorhynchs is restricted to the trunk, including mesoderm (muscles) and ectoderm derivated structures (nerves and glands). The nervous system shows a segmental arrangement in the first eight trunk segments, whereas the last three segments show some deviating arrangements most likely related to a post-hatching development of these segments. The presence of non-segmental trunk muscles is interpreted as adaptations for increased introvert motility and trunk flexibility.

中文翻译：

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深入了解泥龙形态（Kinorhyncha，Allomalorhagida）：Dracoderes abei 和 Pycnophyes ilyocryptus 的肌解剖学和神经解剖学

需要进行涵盖后生动物谱系多样性的综合形态学研究，以获得器官系统进化的完整图景。尽管在过去的几十年里对鲜为人知的门类的研究数量有所增加，但这些谱系的知识差距仍然显着。kinorhynchs 或泥龙就是这种情况，其中只有少数属，主要属于主要分支 Cyclorhagida，经过详细的形态学检查。在这里，我们通过免疫化学、CLSM 和计算 3D 重建对 Dracoderes abei 和 Pycnophyes ilyocryptus 的研究，探索了另一个主要进化枝 Allomalorhagida 的神经解剖学和肌解剖学。Dracoderes 目前的系统发育位置是所有剩余的 allomalorhagids 的姊妹组，这使其成为了解 Kinorhyncha 内器官系统进化的关键分类群。在 D. abei 和 P. ilyocryptus 的躯干中发现了清晰的肌肉和神经节段排列，不包括在最后一段中观察到的修改。比较当前和以前对异毛喉科动物和睫状体科动物的研究时，神经系统显示出跨动吻鳄的保守模式，而肌肉组织在属之间显示出显着差异。kinorhynchs 的分割仅限于躯干，包括中胚层（肌肉）和外胚层衍生结构（神经和腺体）。神经系统在前八个躯干节段中呈节段排列，而最后三个部分显示了一些偏离的安排，最有可能与这些部分的孵化后发展有关。非节段性躯干肌肉的存在被解释为对增加的内向运动和躯干灵活性的适应。