Telonemia is a poorly known major phylum of flagellated eukaryotes with a unique combination of morphological traits. Phylogenomics recently revealed the phylogenetic position of telonemids as sister to SAR, one of the largest groups of eukaryotes, comprising Stramenopiles, Alveolata and Rhizaria. Due to this key evolutionary position, investigations of telonemids are of critical importance for elucidating the origin and diversification of an astounding diversity of eukaryotic forms and life strategies. To date, however, only two species have been morphologically characterized from Telonemia, which do not represent this genetically very diverse group. In this study, we established cultures for six new telonemid strains, including the description of five new species and a new genus. We used these cultures to update the phylogeny of Telonemia and provide a detailed morphological and ultrastructural investigation. Our data elucidate the origin of TSAR from flagellates with complex morphology and reconstruction of the ancestral structure of stramenopiles, alveolates and rhizarians, and their main synapomorphic characters. Since telonemids are a common component of aquatic environments, the features of their feeding, behaviour and ecological preferences observed in clonal cultures and the results of global metabarcoding analysis contribute to a deeper understanding of organization of microbial food webs.

The recently discovered Provora supergroup has primarily been examined to determine their phylogenomic position in the eukaryotic tree. Their morphology is more poorly studied, and here we focus on their cellular organization and how it compares with that of other supergroups. These small eukaryovorous flagellates exhibit several ultrastructural features that are also found in a subset of taxa from a wide variety of deep-branching lineages (Stramenopiles, Alveolata, Hemimastigophora, Malawimonadidae, Discoba and Metamonada), including vesicles beneath the plasmalemma, two opposing vanes on the flagella, a ventral feeding groove and a fibrillar system resembling the excavate type. Additionally, we identified four main microtubular roots (r1–r4) and a singlet root between r1 and r2, which support the strong feeding apparatus resembling ‘jaws’. Their unique extrusive organelles (ampulosomes) have a similar organization to Hemimastigophora extrusomes, but most of their cell characteristics most closely resemble features of the TSAR + Haptista grouping. We also describe a new species, Nibbleromonas piranha sp. nov., and highlight features of its feeding behaviour, which can be so aggressive as to result in cannibalism.

Predatory flagellated protists remain extremely poorly studied but often represent the most important deep-branching lineages of eukaryotic evolution. One of the most enigmatic and poorly studied predatory protist groups is Rhodelphidia. These are heterotrophic flagellates, yet belong to the primarily photosynthetic supergroup Archaeplastida and are related to red algae in particular. Here, we describe a new rhodelphid species and the first known soil representative of this group, Rhodelphis edaphicus sp. nov., which was isolated into a clonal culture from agricultural soil. The novel species actively phagocytoses the cells of other protists and bacteria. Using light and electron microscopy, we examined its morphology and identified several novel features, including complex tripartite mastigonemes—not previously reported for this taxon—which link rhodelphids with Cryptista. We expanded a previous 18S rRNA dataset for rhodelphids with environmental sequences and revealed the presence of a soil clade to which the new species belongs. A search of soil metabarcoding data yielded several unknown rhodelphid lineages. Analysis of the distribution of known species and environmental DNA data revealed that rhodelphids inhabit diverse geographic locations worldwide and are found in a variety of habitats, including marine and fresh waters, soils, and, most likely, anaerobic bottom sediments near fumaroles. The diversity of modern rhodelphid habitats, including soil ecosystems, highlights the different environments in which early stages of Archaeplastida evolution may have occurred. The identification and comprehensive study of new lineages of basal archaeplastids provides new insights into the complex evolutionary processes associated with early eukaryotic radiation, the emergence of photosynthesis and plastid evolution that gave rise to the diversification of numerous forms of algae and land plants.