Strausfeld Nicholas J, Andrew David R, Hou Xianguang, Hirth Frank
Department of Neuroscience, University of Arizona, Tucson, AZ, 85721, USA.
Department of Biology, Lycoming College, Williamsport, PA, 17701, USA.
Nat Commun. 2025 Aug 28;16(1):7938. doi: 10.1038/s41467-025-62849-w.
Cambrian fossils from the Chengjiang biota demonstrate that over half a billion years ago early stem euarthropods existed coevally with representatives of already recognizable crown groups. Prominent stem taxa were Fuxianhuia protensa and Alalcomenaeus whose cerebral and ganglionic traits identify them as, respectively, stem mandibulates and stem chelicerates. Here we report on the visual systems and brain of the enigmatic lower Cambrian euarthropod Jianfengia multisegmentalis, which reveals neural traits suggestive of Pancrustacea despite its possession of 'great appendages'. As occur in pancrustaceans, three nested optic neuropils are resolved in the eyestalks of Jianfengia, together with rostral ocelli and their associated nerves supplying a discrete forebrain region. Sutured eyestalks typifying crown Malacostraca provide compound eyes populated by ommatidia revealing structures suggesting cone-building cells. These and other neuroanatomical traits provide a powerful tool for resolving euarthropod relationships. Phylogenetic analyses deploying neural traits of Jianfengia, other Cambrian taxa, and extant Euarthropoda elucidate the status of Jianfengia as sister to total Mandibulata and reveal the short-bodied 'great appendage' Leanchoiliidae as sister to total Chelicerata. Together these data provide independent evidence for a 23 year-old proposition that 'great appendage' morphology defines the early stem from which derived the two branches of the euarthropod tree of life.
来自澄江生物群的寒武纪化石表明，在超过5亿年前，早期的真节肢动物干群就已经与一些已然可辨认的冠群代表同时存在。突出的干群分类单元有延长抚仙湖虫和迷人林乔利虫，它们的脑和神经节特征分别将它们鉴定为干群有颚类和干群螯肢类。在此，我们报告了寒武纪早期神秘的多节尖峰虫的视觉系统和脑，它揭示了一些神经特征，表明其属于泛甲壳动物，尽管它拥有“大附肢”。如同在泛甲壳动物中一样，在尖峰虫的眼柄中可分辨出三个嵌套的视神经节，还有位于吻部的单眼及其相关神经，这些神经通向一个离散的前脑区域。典型的冠群软甲纲动物的缝合眼柄中有由小眼组成的复眼，这些小眼的结构表明存在造锥细胞。这些以及其他神经解剖学特征为解析节肢动物之间的关系提供了有力工具。利用尖峰虫、其他寒武纪分类单元以及现存节肢动物的神经特征进行的系统发育分析，阐明了尖峰虫作为整个有颚类姐妹群的地位，并揭示了短体的“大附肢”奇虾科动物是整个螯肢类的姐妹群。这些数据共同为一个23年前提出的观点提供了独立证据，即“大附肢”形态定义了节肢动物生命树两个分支所起源的早期干群。
