Abstract
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.
Highlights
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HF-25 isolated from the permafrost of the Kolyma Lowland, cells with similar morphology were found in the soil samples from Crimea, an island on the Dnieper River, and in the wet moss with sand from Franz Josef Land archipelago (Figure 4)
We propose that the strain HF-25 represents a new genus and species of centrohelid heliozoans due to its isolated placement on the phylogenetic tree and the unique morphology of silica scales
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Several centrohelid genera can lose silica scales and produce radial needle-shaped organic spicules in clonal cultures [7,8] making morphology-based species identification more challenging. Described representatives of this group have various cell sizes, from 3 μm in Choanocystis minima Zlatogursky, 2010 to 150 μm in Acanthocystis turfacea Carter, 1863, which allows them to occupy different niches in microbial food webs. Based on 18S rRNA gene sequencing of cultured strains and environmental sequences, it was suggested that the 130 morphospecies represent only 10% of the centrohelid diversity to date [12]. We describe the novel Triangulopteris lacunata gen. et sp. nov., a representative of the Pterista lineage
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