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.