Silica‐scaled heterotrophic protists Rotosphaerida, Thaumatomonadida, and Centroplasthelida in the large continuous ecosystem connecting Lake Baikal to the Kara Sea

Abstract

Heterotrophic protists Rotosphaerida, Thaumatomonadida, and centrohelid heliozoans are among the less studied silicified protists in terms of their biogeography and ecology. These organisms inhabit fresh and brackish water, and leave behind siliceous structural elements after death that are species‐specific and amenable to electron microscopic analysis. This paper is the first to present data on species richness and taxonomic structure of silica‐scaled heterotrophic protists—rotosphaerids, colorless free‐living thaumatomonad flagellates and centrohelid heliozoans—in the large continuous water system of Siberia connecting Lake Baikal to the Kara Sea. In the study area, electron microscopy revealed 21 centrohelid heliozoan species from the genera Raphidiophrys (1), Acanthocystis (7), Choanocystis (3), Raineriophrys (2), Raphidocystis (6), and Pterocystis (2), seven rotosphaerid species from the genera Pinaciophora (3), Turriplaca (2), Rabdiophrys (1), and Pompholyxophrys (1), and one thaumatomonad flagellate species Thaumatomastix. Two species of rotosphaerids, Rabdiophrys cf. anulifera and Pinaciophora tridentata, and two species of centrohelid heliozoans, Acanthocystis cf. tubata, and A. cf. cornuta, were found in the waters of Russia for the first time. The most widespread species in fresh water from Lake Baikal to the Lower Yenissei River were Pinaciophora fluviatilis and Raineriophrys cf. fortesca. These species disappeared from the protist assemblages of the Yenissei gulf of the Kara Sea due to higher salinity, with only three species, Acanthocystis cf. mylnikovi (at 3.12‰ salinity) and A. pectinata and Raphidocystis sp. 2 (at 8‰ salinity), found in the area. The sensitivity of silica‐scaled heterotrophic protists to changes in habitat parameters suggests that these microeukaryotes could be new indicator organisms.

On the Biology, Diversity and Evolution of Nucleariid Amoebae (Amorphea, Obazoa, Opisthokonta1

“…Most nucleariid amoebae live in freshwater environments, but are also found in marine settings (Lithocolla) and even faeces (Fonticula) (Table 1). Distribution and diversity information is available from isolation and fresh sample observations (e.g., Penard (1904)), sampling of scales/coverings visualised with electron microscopy (e.g., Bessudova et al (2022)), and molecular metabarcoding analyses (e.g., del ). Such studies are fundamental for understanding the biology and taxonomy of protists.…”

“…The diversity of covered nucleariids is mostly known from morphological studies of fresh samples, never from cultures. Pompholyxophrys, with seven described morphospecies based on the shape of their silica pearls, may be seasonal and more restricted to clear freshwater bodies, wet Sphagnum moss, and 'pristine' peat bogs (Bessudova et al 2022;Leonov 2012;Roijackers and Siemensma 1988;Wujek 2015). Recently, several single cells of Pompholyxophrys were isolated (Galindo et al 2019).…”

“…Still, there are at least four genera of silica-scaled filose amoebae that could be part of the nucleariid diversity: Pinaciophora, Rabdiophrys, Rabdiaster, and Thomseniophora (Table 2). During the expansion of electron microscopy, starting from the last quarter of the past century, scientists have characterised siliceous scales associated with silica-covered nucleariids from marine and freshwater environments, mostly without observing whole cells (Bessudova et al 2022;Croome et al 1987;Esteban et al 2007;Nicholls and Dürrschmidt 1985;Thomsen 1978;Wujek 2015). However, as these studies are not always based on the observation of living cells, the results may have certain limitations.…”

“…Since then, most molecular studies have been using Cristidiscoidea sensu Cavalier-Smith, only including Nuclearia or environmental sequences (Amaral-Zettler et al 2002;Arroyo et al 2018;del Campo et al 2015;Couradeau et al 2011;Heger et al 2018;Torruella et al 2015). Meanwhile, Rotosphaerida sensu Mikrjukov has been used during the study of scale-bearing filose amoebae from a morphological point of view (Bessudova et al 2022;Croome et al 1987;Esteban et al 2007;Nicholls and Dürrschmidt 1985;Roijackers and Siemensma 1988;Thomsen 1978;Wujek 2015), and more recently to include both uncovered and covered filose amoebae (Adl et al 2019;Galindo et al 2019).…”

Silica scaled Protista and Stomatocysts in East Siberia

“…In July 2018 in the floodplains of the Selenga and Barguzin rivers, a continuous period of low water was interrupted by high water. A study of the waters during this period showed that the species composition of the scaled chrysophytes on the one hand significantly decreased (to 23 species), on the other hand, it was enriched with new species for the Baikal region, amounting to 79 species (Bessudova et al, 2020). After analyzing two years of different water content, we came to the conclusion that the high diversity of scaled chrysophytes in the mouths of the main tributaries of Lake Baikal, Selenga, Upper Angara and Barguzin in low water conditions may be caused by previous floods.…”