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Investigation of large populations of peteinoid acritarchs recovered from Middle Ordovician strata of the Hälludden and Horns Udde quarry sections (Öland, Sweden) allows for statistical analyses based on morphometric measurements. The results indicate the presence of assemblages with a continuous variability of morphotypes, thus a distinction of different peteinoid acritarch taxa in the sections proved to be impossible. This challenges the currently accepted classification based on a differentiation into the three genera Peteinosphaeridium, Cycloposphaeridium and Liliosphaeridium, and a multitude of different species; individual taxa are essentially arbitrary as morphotypes intergrade. Investigations on modern dinoflagellates show that these can develop variable cyst morphologies depending on environmental factors. By analogy, it can be hypothesised that the different morphologies observed among the peteinoid acritarchs from Öland are cysts produced by only very few phytoplanktic organisms (or even a single species) with high morphological variability. [ABSTRACT FROM AUTHOR]

This study documents 'colonial' palynomorphs from the Upper Ordovician Ghelli Formation of north-eastern Iran. The aggregates of organic-walled microfossils come from the Katian Armoricochitina nigerica–Ancyrochitina merga chitinozoan biozones of this formation. The 'colonial' microfossils can be classified as acritarchs and/or cryptospores, but they cannot be attributed to a particular biological group. Some specimens resemble 'thalli' of putative spores, such as Grododowon orthogonalis Strother 2017. Other clusters may suggest an affinity to green algal groups, in particular to colonial chlorophyceaen algae, most probably belonging to Hydrodictyaceae. Some specimens also show morphological similarities with cyanobacterial groups. There is so far no evidence to relate these 'colonial' palynomorphs to primitive land plants, but we hypothesise that they were possibly produced by ancient green algal lineages with some kind of subaerial existence. [ABSTRACT FROM AUTHOR]