Data from: Anatomy and affinities of a new 535-million-year-old medusozoan from the Kuanchuanpu Formation, South China

We describe here Sinaster petalon gen. et sp. nov., a new embryonic form from the c. 535 million-year-old Kuanchuanpu Formation of South China (Ningqiang, Shaanxi Province). The excellent three-dimensional, phosphatic preservation of these microfossils allowed us to use x-ray microtomographic techniques to make accurate reconstructions of their internal structures and to compare their anatomy point-by-point with that of extant cnidarians and other animal groups. Sinaster petalon has anatomical features typical of extant Medusozoa (Cnidaria), such as coronal muscles, perradial and adradial frenula, interradial septa, accessory septa, gonad-lamellae, tentacle buds and perradial pockets. Although Sinaster cannot be straightforwardly assigned to any crown-group within Medusozoa, the presence of marginal lappets and endodermal lamellae suggests that it is closer to Cubozoa and Scyphozoa than to any other group of modern cnidarians. The tentative placement of Sinaster within the stem-group Cubozoa is justified by the presence of a velarium supported by a frenulum. The cubozoan affinities of Sinaster are also supported by cladistic analysis.

本文记述了Sinaster petalon新属新种（Sinaster petalon gen. et sp. nov.），该类化石为产自华南陕西省宁强县、距今约5.35亿年的宽川铺组（Kuanchuanpu Formation）的新型胚胎微化石。
这批微化石以优异的三维磷酸盐化保存状态，使得研究团队可借助X射线显微断层扫描技术（X-ray microtomographic）对其内部结构进行精准重建，并将其解剖特征与现生刺胞动物（Cnidaria）及其他动物类群进行逐点比对。
Sinaster petalon具备现生水母亚门（Medusozoa，刺胞动物门）的典型解剖特征，包括冠状肌、辐位与近辐位系带、间辐射隔膜、副隔膜、生殖层板、触手芽及辐位囊。
尽管该物种无法直接归入水母亚门的任一冠群（crown-group），但其拥有边缘叶瓣与内胚层板的特征表明，相较于其他现生刺胞动物类群，它与立方水母纲（Cubozoa）和钵水母纲（Scyphozoa）的亲缘关系更为接近。
基于其具有系带支撑的缘膜（velarium）这一关键特征，本研究将Sinaster petalon暂置于立方水母纲的干群（stem-group）中，该分类位置具备合理性。
支序分类分析（cladistic analysis）同样支持Sinaster petalon与立方水母纲的亲缘关联。