@inproceedings{01H5302SPNQBPYQ1G21VYAR2VN,
  abstract     = {{The acritarch genus Radiosperma was originally described as an “enigmatic organism” by the Belgian biologist Alphonse Meunier (1857-1918). Two species were described: R. corbiferum from Arctic waters and R. textum from the Belgian coast (Meunier 1910, 1919). It has been widely reported from plankton and sediments since the late 19th century, with suggested biological affinities ranging from invertebrate eggs to tintinnids.
The genus description is now improved and both congeners are redescribed (Gurdebeke et al. 2023). Based on SSU and LSU rRNA sequences, Radiosperma textum is shown to be a ciliate cyst related to the ciliate genus Askenasia and positioned among the classes Prostomatea, Plagiopylea and Oligohymenophorea. Radiosperma is considered closely related to Hexasterias and Halodinium, two former acritarchs that were assigned previously to the ciliophora (Gurdebeke et al. 2018).
The spatiotemporal distribution and ecology of both species are discussed, revealing a common confusion in species assignment by most authors. R. corbiferum appears limited to Arctic waters and the Baltic Sea, while R. textum is found in temperate coastal waters in other parts of the world. The chemical composition is documented based on micro-Fourier Transform Infrared spectroscopy. Its refractory nature provides potential for fossilization and applicability as indicator of freshwater influence in palynological studies.
In addition, newly obtained SSU and LSU rRNA sequences for several flask shaped ciliate cysts (e.g., Fusopsis and Strombidium) are also included in the phylogenetic analysis and the occurrence of fossilizable cysts in the ciliophoran clade in the marine environment is reviewed. It is confirmed that ciliate cyst morphology has taxonomic significance and that morphological identification of cysts can be reliable. Further elucidating cyst stages in ciliate life cycles will improve understanding of ciliate biology and ecology and their applicability as (paleo)environmental tracers.

References
Gurdebeke, P.R., Mertens, K.N., Takano, Y., Yamaguchi, A., Bogus, K., Dunthorn, M., Matsuoka, K., Vrielinck, H., Louwye, S., 2018. The affiliation of Hexasterias problematica and Halodinium verrucatum sp. nov. to ciliate cysts based on molecular phylogeny and cyst wall composition. European Journal of Protistology 66, 115–135.
Gurdebeke, P.R., Mertens, K.N., Rajter, L., Meyvisch, P., Potvin, E., Yang, E.J., André, C., Pospelova, V., Louwye, S. 2023. The ciliophoran affinity of Radiosperma textum, and its relation to other marine ciliate cysts. Marine Micropaleontology 178, 102185
Meunier, A., 1910. Microplankton des Mers de Barents et de Kara. Duc d’Orléans. Campagne arctique de 1907. Imprimerie scientifique Charles Bulens: Bruxelles. 355 p. + atlas (XXXVII plates).
Meunier, A.,1919. Microplancton de la Mer flamande. 4me partie. Les Tintinnides et cetera. Mémoires du Musée royal d’Histoire Naturelle de Belgique 8, 59 p.}},
  author       = {{Gurdebeke, Pieter and Mertens, Kenneth Neil and Lubomir, Rajter and Meyvisch, Pjotr and Potvin, Eric and Yang, Eun Jin and André, Coralie and Pospelova, Vera and Louwye, Stephen}},
  booktitle    = {{Book of abstracts : VLIZ Marine Science Day 2023}},
  issn         = {{1377-0950}},
  keywords     = {{Diversity,Taxonomy,Ciliophora,Micro-FTIR,LSU and SSU rDNA,Acritarch}},
  language     = {{eng}},
  location     = {{Bruges, Belgium}},
  pages        = {{63--63}},
  publisher    = {{VLIZ}},
  title        = {{Alphonse Meunier's enigmatic Radiosperma belongs to the ciliates}},
  url          = {{https://dx.doi.org/10.48470/41}},
  volume       = {{90}},
  year         = {{2023}},
}