Xiphosurans are aquatic chelicerates with a fossil record extending into the Early Ordovician and known from a total of 88 described species, four of which are extant. Known for their apparent morphological conservatism, for which they have gained notoriety as supposed ‘living fossils’, recent analyses have demonstrated xiphosurans to have an ecologically diverse evolutionary history, with several groups moving into non-marine environments and developing morphologies markedly different from those of the modern species. The combination of their long evolutionary and complex ecological history along with their paradoxical patterns of morphological stasis in some clades and experimentation among others has resulted in Xiphosura being of particular interest for macroevolutionary study. Phylogenetic analyses have shown the current taxonomic framework for Xiphosura—set out in the Treatise of Invertebrate Paleontology in 1955—to be outdated and in need of revision, with several common genera such as Paleolimulus Dunbar, 1923 and Limulitella Størmer, 1952 acting as wastebasket taxa. Here, an expanded xiphosuran phylogeny is presented, comprising 58 xiphosuran species as part of a 158 taxon chelicerate matrix coded for 259 characters. Analysing the matrix under both Bayesian inference and parsimony optimisation criteria retrieves a concordant tree topology that forms the basis of a genus-level systematic revision of xiphosuran taxonomy. The genera Euproops Meek, 1867, Belinurus König, 1820, Paleolimulus, Limulitella, and Limulus are demonstrated to be non-monophyletic and the previously synonymized genera Koenigiella Raymond, 1944 and Prestwichianella Cockerell, 1905 are shown to be valid. In addition, nine new genera (Andersoniella gen. nov., Macrobelinurus gen. nov., and Parabelinurus gen. nov. in Belinurina; Norilimulus gen. nov. in Paleolimulidae; Batracholimulus gen. nov. and Boeotiaspis gen. nov. in Austrolimulidae; and Allolimulus gen. nov., Keuperlimulus gen. nov., and Volanalimulus gen. nov. in Limulidae) are erected to accommodate xiphosuran species not encompassed by existing genera. One new species, Volanalimulus madagascarensis gen. et sp. nov., is also described. Three putative xiphosuran genera—Elleria Raymond, 1944, Archeolimulus Chlupáč, 1963, and Drabovaspis Chlupáč, 1963—are determined to be non-xiphosuran arthropods and as such are removed from Xiphosura. The priority of Belinurus König, 1820 over Bellinurus Pictet, 1846 is also confirmed. This work is critical for facilitating the study of the xiphosuran fossil record and is the first step in resolving longstanding questions regarding the geographic distribution of the modern horseshoe crab species and whether they truly represent ‘living fossils’. Understanding the long evolutionary history of Xiphosura is vital for interpreting how the modern species may respond to environmental change and in guiding conservation efforts.

中文翻译：

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Xiphosura的系统发育和系统学

Xiphosurans 是一种水生螯肢动物，其化石记录延伸到早奥陶世，已知共有 88 种描述的物种，其中四种现存。以其明显的形态保守主义而闻名，因此它们被称为所谓的“活化石”，最近的分析表明，xiphosurans 具有生态多样化的进化历史，有几个群体进入非海洋环境并发展出与现代物种。它们漫长的进化和复杂的生态历史，以及它们在一些进化枝中形态停滞的矛盾模式和其他实验的结合，导致 Xiphosura 对宏观进化研究特别感兴趣。系统发育分析表明，1955 年《无脊椎动物古生物学论文》中提出的 Xiphosura 当前分类框架已经过时并需要修订，其中几个常见属，如 Paleolimulus Dunbar，1923 和 Limulitella Størmer，1952 年作为废纸篓分类群. 在这里，展示了扩展的 xiphosuran 系统发育，包括 58 个 xiphosuran 物种，作为编码为 259 个字符的 158 个分类群螯合物矩阵的一部分。在贝叶斯推理和简约优化标准下分析矩阵，检索出一致的树形拓扑结构，该拓扑结构构成了 xiphosuran 分类学的属级系统修订的基础。Euproops Meek 属，1867，Belinurus König，1820，Paleolimulus、Limulitella 和 Limulus 被证明是非单系的，之前同义的 Koenigiella Raymond 属，1944 和 Prestwichianella Cockerell, 1905 被证明是有效的。此外，还有九个新属（Belinurina 中的 Andersoniella gen. nov.、Macrobelinurus gen. nov. 和 Parabelinurus gen. nov.；Paleolimulidae 中的 Norilimulus gen. nov.；Batracholimulus gen. nov. 和 Boeotiaspis gen. nov. 在 Austrolimulidae 中；和 Allolimulus gen. nov.、Keuperlimulus gen. nov. 和 Volanalimulus gen. nov. in Limulidae) 被竖立以容纳现有属不包括的 xiphosuran 物种。一新种，Volanalimulus madagascarensis gen。等 sp. 11 月，也有描述。三个假定的 xiphosuran 属 - Elleria Raymond, 1944、Archeolimulus Chlupáč, 1963 和 Drabovaspis Chlupáč, 1963 - 被确定为非 xiphosuran 节肢动物，因此从 Xiphosura 中移除。Belinurus König, 1820 优先于 Bellinurus Pictet, 1846 也得到证实。这项工作对于促进 xiphosuran 化石记录的研究至关重要，并且是解决有关现代鲎物种地理分布以及它们是否真正代表“活化石”的长期问题的第一步。了解 Xiphosura 的悠久进化历史对于解释现代物种如何应对环境变化和指导保护工作至关重要。