The ciliophoran affinity of Radiosperma textum, and its relation to other marine ciliate cysts

The acritarch genus Radiosperma has been reported from plankton and sediments since the late 19th century, with suggested biological affinities ranging from invertebrate eggs to tintinnids. Here, the genus description is improved and its two species, Radiosperma corbiferum and Radiosperma textum, are redescribed. Radiosperma textum is shown to be a ciliate cyst related to Askenasia based on new SSU and LSU rRNA sequences. The spatiotemporal distribution and ecology of both species are discussed. The chemical composition is documented based on micro-Fourier Transform Infrared spectroscopy. Furthermore, new SSU and LSU rRNA sequences for several flask shaped ciliate cysts (Fusopsis, Strombidium) are also included in the analysis and the occurrence of fossilizable cysts in the ciliophoran clade is reviewed.