A. P. Myl’nikov

Biology and morphology of freshwater rapacious flagellate Colponema aff. loxodes Stein (Colponema, Alveolata)

The biology, morphology, and ultrastructure of the freshwater rapacious flagellate Colponema aff. loxodes, which attacks bodonids and chrysomonads, are studied. The flagellate is characterized by three-membrane alveolar pellicle, vesicular nucleus, two heterodynamous flagella, two microtubule bands which armor the longitudinal groove, and mitochondria with tubular cristae. Toxicysts (thread-organelles) are found in the cytoplasm. The posterior flagellum is characterized by the proximal fold. Micropores are completely absent. After being caught, the prey is taken into the longitudinal groove. Vegetative swimming cells are present in the life cycle. No reproduction or latent cysts are found. The taxonomical position of Colponema aff. loxodes is discussed in comparison with other colponemids and protists.

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. is considered. The cell is surrounded by two-layered triangular scales. They are formed on the surface of mitochondria. Pseudopodia grabbing bacteria run from ventricular furrow, which is armored with two longitudinal bands of microtubules. Heterodynamic flagella run from small flagellar pocket. Long back flagellum has thin mastigonemes. Proximal area of short flagellum is covered with flat oval scales. Transitional flagellant zone has no spiral or other additional elements. Transverse plate is localized above cell surface. Kinetosomes are parallel to each other. Vesicular nucleus and Golgi apparatus have typical structure. Oval mitochondria contain tubular cristae. Within cytoplasm, extrusive organelles (kinetocysts) containing amorphous material and capsule were found. The latter consists of muff and cylinder. Plasmodial and cystic phases of development have not been discovered. Contractile vacuole is absent. The resemblance between Thaumatomastix sp. and other thaumatomonads has been discussed.

Ultrastructure of the marine predatory flagellate Metromonas simplex Larsen et Patterson, 1990 (Cercozoa)

The ultrastructure of the marine predatory flagellate Metromonas simplex Larsen et Patterson was studied. The cell is surrounded by a low-contrast fibrous layer composed of thin hairs covered by a thin bilayer membrane and an outer layer of thin short fibers. The plasmalemma lies under these layers. The predator captures whole cells of the prey, usually bodonids or chrysomonads. The cytostome as a cell pocket is undetectable. The long flagellum bears very thin mastigonemes (hairs) with lengths of 0.8–1.0 μm; the short flagellum is naked and reduced in length. The transitional zone lacks spirals or other additional elements. The transversal plate is elevated on the cell surface. The flagellar root system is very simple and has one microtubular band which originates near the kinetosomes. The latter are parallel to each other and interconnected by fibrous bridges. The vesicular nucleus, Golgi apparatus, and endoplasmic reticulum are of typical structures. The oval mitochondria of 0.6–2.5 μm contain lamellar cristae. The cylindrical extrusomes (trichocysts) found in the cytoplasm have lengths of 1.0–1.4 μm and diameters of 0.12–0.08 μm. The trichocysts have a wheel-shaped structure with 13 spokes visible in cross-sections. The contractile vacuole is absent. The similarity that M. simplex shares with Metopion fluens Larsen et Patterson, cryothecomonads, and other predatory flagellates is discussed.

The morphology of predatory flagellate Colpodella pseudoedax Mylnikov et Mylnikov, 2007 (Colpodellida, Alveolata)

The structure of the predatory freshwater flagellate Colpodella pseudoedax was studied. The cell was found to contain two heterodynamic flagella, three-membrane pellicle, micropores, subpellicular microtubules, microtubular open-side conoid, roptries, micronemes, extrusive organelles (trichocysts), and mitochondria with vesicular and tubular cristae. Upon discharge, trichocysts form cross-striated bands. A thin-walled cylinder lies in the transitional zone of the flagella. Cells reproduce by means of longitudinal binary fission. This species differs from similar C. edax by their smaller cell size and lack of reproduction cyst. Similarities between C. pseudoedax and other colpodelids, as well as between colpodellids and perkinseids and sporozoans, are discussed.

Changes in biological characteristics of freshwater heterotrophic flagellates and cladocerans under the effect of metal oxide nano- and microparticles

Data on the effect of nano- and microparticles of cerium and titanium dioxides and zinc oxide on the survival rate and reproduction of nanoflagellates and ceriodaphnia are given. The inhibitory effect of metal oxide nanoparticles on nanoflagellates Bodo saltans Ehrenberg manifested itself in a decrease in their population after 3–4 days of exposure. This effect was found to increase with agent concentrations. In the case of Ceriodaphnia affinis Lilljeborg, their reproductive characteristics showed a significant correlation with the concentrations of nanosize particles of the substances under consideration. Unlike zinc oxide, the microrparticles of titanium and cerium dioxides were less toxic than the respective nanoparticles.

The influence of cryogenic mass exchange on the distribution of viable microfauna in cryozems

The role of cryogenic mass exchange in the distribution of the viable microfauna (ciliates, heterotrophic flagellates, and nematodes) in the profiles of cryoturbated cryogenic soils and in the upper layers of permafrost was revealed. The material for microbiological investigations was collected from the main horizons of cryozem profiles, including the zones with morphologically manifested processes of cryogenic mass exchange (the development of barren spots, cryoturbation, and suprapermafrost accumulation) and the zones affected by solifluction. The radiocarbon dating of the soil samples showed that the age of the organic cryogenic material and material buried in the course of solifluction varied from 2100 to 4500 years. Some zones with specific ecological conditions promoting the preservation of species diversity of the microfauna were found to develop in the cryozem profiles. A considerable part of the community (38% of ciliates, 58% of flagellates, and 50% of nematodes) maintained its viability in the dormant state, and in some cases, it could pass to the state of long-term cryobiosis in the upper layer of permafrost.

The cell structure of the reticulopodial amoeba Filoreta marina Bass et Cavalier-Smith (Cercozoa)

The cell structure of a reticulopodial amoeba, Filoreta marina Bass et Cavalier-Smith, is described. The cell is covered by a unitary membrane; glycostyles are absent. The life cycle comprises the uninucleate stage, multinucleate plasmodium, and spherical uninucleate cysts. The microtubules inside pseudopodia and the flagella are absent. The vesicular nuclei, endoplasmic reticulum, and Golgi apparatus are of a typical structure. The plasmodium produces a branched network of narrow anastomosing (reticulopodia) and wide pseudopodia. Thin unbranched micropseudopodia have also been observed. Oval mitochondria with a size of 0.3 × 0.6 μm contain the tubular cristae. A bidirectional motion of the cytoplasm inside the reticulopodia has been detected. Extrusomes (extrusive organelles) have not been found. The contractile vacuole is absent. F. marina feeds on bacteria. A similarity of this amoeba to other filose and reticulopodial amoebas is discussed.

Choanocystis antarctica sp. n., a new heliozoan (Centrohelida) species from the littoral zone of King George Island, South Shetland Islands, Antarctica

The morphology of a new marine heliozoan from the sandy littoral of King George Island (the South Shetland Islands, Antarctica) is described. The species is characterized by bent or curved spicules with a spur at the shaft bend point. Similarities and differences between the new species and other representatives of the genus Choanocystis are considered.

Structure of the cell of the amoeboid flagellate Thaumatomonas coloniensis Wylezich et al., 2007 (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of the amoeboid flagellate Thaumatomonas coloniensis Wylezich et al. has been studied. The cell is surrounded by somatic scales forming on the surface of the mitochondria. The heterodynamic flagella emerge from the small flagellar pocket. Both flagella are covered by pineal scales and thin twisted mastigonemes. The kinetosomes lie parallel to each other. The transitional zone of the flagella carries the thin-walled cylinder. The transversal plate of the flagella is above the cell surface. The flagellar root system consists of three microtubular bands and a fibrillar rhizoplast. The vesicular nucleus and Golgi apparatus are of the usual structure. The mitochondria contain tubular cristae. The extrusive organelles (kinetocysts) contain amorphous material and a capsule; they are located in cytoplasm. The capsule consists of a muff and cylinder. Osmiophilic bodies of various shapes contain crystalloid inclusions. The pseudopodia capturing the bacteria emerge from the ventral groove. The groove is armored by the two longitudinal groups of the close situated microtubules. Microbodies and symbiotic bacteria have not been discovered. The resemblance of Th. coloniensis with other thaumatomonads is discussed.

First records of centrohelid heliozoans (Centrohelida) in Mongolia

Species composition, distribution, and morphological characters of centrohelid heliozoans (Centrohelida) in fresh lentic and lotic waterbodies of Mongolia have been studied using scanning electron microscopy methods. Six species of the families Raphidiophryidae Mikrjukov, 1996 and Acanthocystidae Claus, 1874 have been recorded in this region for the first time. The morphology of the heliozoans mostly matches the available published descriptions. The recorded species are described and figured.