Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian.

中文翻译：

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早寒武世澄江生物群中的刺胞动物 (Cnidaria)

刺胞动物在系统发育上位于“动物之树”的基部附近，它们的早期进化对两侧对称动物的兴起产生了深远的影响。然而，这种“低等”后生动物进化枝的早期多样性和系统发育迄今一直是个谜。幸运的是，早期寒武纪的刺胞动物化石可以提供对其进化史的重要见解。在这里，基于对所谓的 hyolith Burithes yunnanensis Hou等人的审查。从华南早期寒武纪澄江生物群中，我们揭示了该物种具有不同于典型软岩的特征，尤其是具有单个开口的漏斗状胃血管系统，嘴周围有一圈触须，并且缺乏鳃盖。这些特征表明与Burithes属的原始定义存在很大差异，并且与刺胞动物的亲缘关系更近。因此，我们将该材料重新分配给一个新属：Palaeoconotuba。基于新解剖特征的系统发育贝叶斯推断确定了一个新的进化枝，包括Palaeoconotuba和Cambrorhytium，作为无柄水母刺胞动物的一个干群，它们通过发育有机锥形膜和漏斗状胃血管系统的突触结合在一起。这项研究揭示了在寒武纪早期进化出终生圆锥膜的水母动物的茎谱系。