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.

本文记述了新属新种花瓣星状胚（Sinaster petalon gen. et sp. nov.），这是一种产自中国华南地区陕西省宁强县约5.35亿年前宽川铺组（Kuanchuanpu Formation）的新型胚胎化石。这些微化石以优异的三维磷酸盐化保存状态，使得我们能够借助X射线显微断层扫描（X-ray microtomographic）技术对其内部结构进行精准重建，并将其解剖结构与现生刺胞动物（cnidarians）及其他动物类群逐点比对。花瓣星状胚具有现生水母亚门（Medusozoa，刺胞动物门）典型的解剖学特征，包括冠状肌、辐缘系带与近辐缘系带、间辐射隔片、副隔片、生殖腺瓣、触手芽以及辐向口袋。尽管无法将花瓣星状胚直接归入水母亚门内的任何冠群，但其具有边缘叶瓣和内胚层瓣的特征表明，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）的亲缘关系更近。基于由系带支撑的缘膜这一特征，将花瓣星状胚暂置于立方水母纲干群的处理方式是合理的。花瓣星状胚与立方水母纲的亲缘关系同样得到了支序分类分析（cladistic analysis）的支持。