A new genus and species of centrohelid heliozoans, Triangulopteris lacunata gen. et sp. nov. (Pterocystidae Cavalier-Smith and Heyden, 2007), from four geographically remote locations (the Crimean Peninsula, the Dnieper Lowland (the East European Plain), Franz Josef Land, and the Kolyma Lowland (North–Eastern Siberia) was examined using light and electron microscopy. The novel centrohelid is characterized by round shape, 4.3–16.3 μm in diameter, covered with two types of scales: 1.06–4.54 μm long triangular spine scales and 1.22–2.05 μm oval plate scales. Studied centrohelid heliozoan possesses a unique spine scale morphology. The base of scales is represented by a horse hoof-shaped basal plate. The inner surface and lateral wings of spine scales have numerous radial ribs with two ‘pockets’ that are located on both sides of the spine shaft. These pockets are formed by the lateral wings and ends of the basal plate. The cyst formation and transition to a spicules-bearing stage were noted. Additionally, phylogenetic tree was constructed based on SSU rRNA sequences including the strain HF-25 from the permafrost of Kolyma Lowland. The resulting phylogeny recovered it within the clade Pterista, while forming a separate sister lineage to H2 clade, which only had included freshwater environmental sequences.

Saline and hypersaline waters are one of the most peculiar ecosystems of our planet, characterized by extreme life conditions. Despite their worldwide distribution, the diversity and abundance of protist communities in these ecosystems remain poorly studied. Here, we analyze planktonic communities of protists sampled across 38 saline and hypersaline water environments (2–390‰) from arid climatic zones of the South Urals and Crimea in light of environmental data using high-throughput 18S rDNA amplicon sequencing. A total of 9 eukaryotic supergroups, 34 phyla, 104 classes, 184 orders, 315 families and 548 genera have been identified. We revealed significant differences in the taxonomic structure of protist communities depending on salinity, geographic location and pH. The protist communities demonstrated linear regression of richness and diversity and growth of the percentage of unclassified Eukaryota (up to 43%) with the increase in salinity. Centrohelids demonstrated the ability to inhabit a broad range of salinities, up to 320‰, which is four times higher than previously reported. Centrohelid species Pinjata ruminata and Yogsothoth sp. are assumed to be specifically adapted to salinity of 3–210‰. The obtained results provide insight into the taxonomy and diversity of protists in saline and hypersaline environments and highlight the great potential for the discovery of new taxa due to the large number of unclassified 18S rDNA sequences.

The species diversity, distribution, and morphological features of centrohelid heliozoans (Centroplasthelida) (Haptista: Centroplasthelida Febvre-Chevalier et Febvre, 1984) from freshwaters of Central and Southern Vietnam have been studied using scanning electron microscopy (SEM). Twelve species, belonging to Acanthocystidae, Choanocystidae, Pterocystidae, Raphidiophryidae, and Raphidocystidae families, have been found. Eleven species are new for Vietnam. Illustrated descriptions of species found are provided. The morphology of investigated centrohelids mainly corresponds to published data; however, some differences have been shown. The diversity of heliozoans in Vietnam and other regions has been discussed.