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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.

Fourier-transform infrared (FTIR) spectroscopy is a spectrochemical technique able to retrieve macromolecular information from organic materials. When combined with a microscope (micro-FTIR), the bulk (geo)chemical composition of single specimen dinoflagellate cysts (dinocysts) can be determined. Micro-FTIR studies on dinocysts are sparse, partially due to the complexity of the method in terms of possible disruptive variables and the interpretability of the data it provides. Nevertheless, it can be a powerful, rapid, and relatively low-cost tool for retrieving macromolecular information from small organic particles. That is, if a certain degree of methodological insights and control can be ensured. This recently led to the development of a methodological framework (Meyvisch et al. 2021) wherein a wide array of variables are discussed. The result of this study is a method based on attenuated total reflection (ATR) micro-FTIR spectroscopy which allows for the collection of robust spectrochemical datasets, and which will be presented here. Earlier micro-FTIR studies on dinocysts have explored the potential of the method to be used as a chemotaxonomical tool (Bogus et al. 2012), a proxy for trophic affinity (Bogus et al. 2014) and to assess preservation of organic matter in oxic and sulphidic depositional environments (Versteegh et al. 2020). Within the light of the later developed methodological framework, some of these authors’ findings are re- evaluated and supplemented with more elaborate and robust datasets. The overview provided on the current state of this – relatively underexplored – research domain perfectly sets the stage to discuss its future perspectives, with a focus on providing answers to major standing questions regarding the (geo)chemical nature and variability of dinoflagellate cyst walls. Finally, other useful and complementary analytical methods which can contribute to elucidating these problems will be briefly discussed.

Supplemental material, sj-pdf-1-asp-10.1177_00037028211041172 for Attenuated Total Reflection (ATR) Micro-Fourier Transform Infrared (Micro-FT-IR) Spectroscopy to Enhance Repeatability and Reproducibility of Spectra Derived from Single Specimen Organic-Walled Dinoflagellate Cysts by Pjotr Meyvisch, Pieter R. Gurdebeke, Henk Vrielinck, Kenneth Neil Mertens, Gerard Versteegh and Stephen Louwye in Applied Spectroscopy

Fourier-transformed infrared (FTIR) spectroscopy is a spectrochemical technique able to retrieve macromolecular information from organic materials. When combined with a microscope (micro-FTIR), the (geo)chemical composition of single specimen dinoflagellate cysts (dinocysts) can be determined. Over the last decades a small number of dinocyst micro-FTIR studies booked often inconsistent results by overlooking important methodological aspects during analysis. This study takes into account variables like sample preparation, specimen morphology and size and spectral data processing steps and presents a standardized method based on attenuated total reflectance (ATR) micro-FTIR spectroscopy which is able to collect robust spectral datasets. These datasets are largely devoid of nonchemical artifacts inherent to other infrared spectrochemical methods which have typically been used in similar studies in the past (i.e. transmission and transflection spectroscopy). Several guidelines are proposed which facilitate the collection and qualitative interpretation of highly reproducible and repeatable spectrochemical dinocyst data. These, in turn, pave the way for a systematic exploration of dinocyst chemistry and its assessment as a chemotaxonomical tool or proxy. An ATR micro-FTIR case study on morphologically similar late Paleogene to early Neogene dinocysts Palaeocystodinium golzowense, Svalbardella clausii and Svalbardella cooksoniae is also presented, which highlights the chemotaxonomical potential of the method.

Additional file 1: This additional file contains supplementary information to the main text and consists of supplementary text, table S1, figure S1 and S2. Supplementary text includes additional methodological descriptions and results. The additional methodological descriptions contain a description of sampling procedures, technical information on how aquaria were set up, extended experimental procedures that were required by ampullariid biology, information for reproducibility of morphometric data collecting, and descriptions of the models that were used in model-based clustering. Additional results consist of direct observations on the reproduction of Lanistes. Table S1. Results of E-tests of multivariate normality per morphospecies and generation. Figure S1. Comparison of the morphospace occupation reconstructed by non-metric multidimensional scaling (nmMDS) in 2 and 3 dimensions along nmMDS1 and 2, with vectors representing how individual specimens are displaced from the 3D configuration to the 2D configuration. Figure S2. Geometric morphometric shape changes along nmMDS1 and 2.

We present a summary of two round-table discussions held during two subsequent workshops in Montreal (Canada) on 16 April 2014 and Ostend (Belgium) on 8 July 2015. Five species of the genus Achomosphaera Evitt 1963 and 33 of the genus Spiniferites Mantell 1850 emend. Sarjeant 1970 occuring in Pliocene to modern sediments are listed and briefly described along with remarks made by workshop participants. In addition, several holotypes and topotypes are reillustrated. Three species previously assigned to Spiniferites are here considered/accepted as belonging to other genera: Impagidinium inaequalis (Wall and Dale in Wall et al. 1973) Londeix et al. 2009, Spiniferites? rubinus (Rossignol 1962 ex Rossignol 1964) Sarjeant 1970, and Thalassiphora balcanica Balteş 1971. This summary forms the basis for a set of papers that follows, where points raised during the workshops are explored in greater detail.

We present a summary of two round-table discussions held during two subsequent workshops in Montreal (Canada) on 16 April 2014 and Ostend (Belgium) on 8 July 2015. Five species of the genus Achomosphaera Evitt 1963 and 33 of the genus Spiniferites Mantell 1850 emend. Sarjeant 1970 occuring in Pliocene to modern sediments are listed and briefly described along with remarks made by workshop participants. In addition, several holotypes and topotypes are reillustrated. Three species previously assigned to Spiniferites are here considered/accepted as belonging to other genera: Impagidinium inaequalis (Wall and Dale in Wall et al. 1973) Londeix et al. 2009, Spiniferites? rubinus (Rossignol 1962 ex Rossignol 1964) Sarjeant 1970, and Thalassiphora balcanica Balteş 1971. This summary forms the basis for a set of papers that follows, where points raised during the workshops are explored in greater detail.