[The morphological study of the cysts Pelomyxa palustris Greeff, 1874].

Pelomyxa palustris Greeff, 1874, is the only species of pelomixoid amoebas with the rest cysts in its life cycle. The morphology of the P. palustris has been studied by the light and electronic microscopy. Encystation of P. palustris under climatic conditions of North-West of Russia occurs within August-September. Rest cysts have a complex, trilaminar wall. Two inner lamina are the dense endocyst and the laminated mesocyst, thickness of each layer runs up to 0.6-0.7 microm. Thickness of the electron-dense ectocyst usually does not exceed 0.1-0.2 microm. The encystated cell of P. palustris has the unique structure. About 60 % of the cell volume are occupied by a huge vacuole placed in the center and filled up with the prokaryotic cytobionts. Different vacuoles, small vesicles of various nature, autophagosomes and lipid drops could be found inside that huge vacuole. The amoebae cytoplasm occupies the space in between endocyst's inner surface and the central vacuole. No any inclusions, prokaryotic cytobionts and most of cell organelles are absent in the cytoplasm. There are 4 large nuclei filled with relatively homogeneous karyoplasm lying in the cytoplasm. Nuclear envelope forms a lot of long tubular channels, running through the cytoplasm and lining the membrane of the central vacuole. Encysted pelomixoid stay in this state up until the beginning of excystation. Excystation of P. palustris in the studied region occurs in spring, during the latter half of April and the beginning of May. Cysts undergo complex morphofunctional changes, related to the reorganization of the wall and formation of young multinucleate amoebas. Only one wall lamina of the 3 initial ones is left up to the moment of excystation. The central vacuole endures ruination and its content penetrates into the cytoplasm. Pelomixoid nuclei divide twice. Prokaryotic cytobionts are localized in cytoplasm and in the perinuclear area. Young multinuclear species of P. palustris coming out of the cysts do not differ in their structure from the adult forms.

[Leptomonas jaculum (Leger, 1902) Woodcock 1914: a leptomonas or a blastocrithidia?].

Flagellates Leptomonas jaculum, inhabiting the intestine of the water scorpion Nepa cinerea posses promastigote organization, typical of the genus Leptomonas. Nevertheless phylogenetic analysis of the 18S rRNA gene revealed that these trypanosomatids form a common phylogenetic clade with cyst-forming representatives of the genus Blastocrithidia. Morphological characters supporting the unity of the group Blastocrithidia + L. jaculum and the probability of including L. oncopelti in it are discussed.

[Development of cyst-like cells of the flagellate Leptomonas oncopelti in the midgut of the hemipteran Oncopeltus fasciatus].

The structure of cyst-like cells of Leptomonas oncopelti (Trypanosomatidae) found in the midgut of the bug Oncopeltus fasciatus (Lygaeidae) was examined with light and electron microscopy. The formation of "cysts" begins with an unequal division of active flagellates with promastigote configuration. Cytokinesis starts on the lateral side of the flagellate, and then the cleavage furrow moves toward the apical end of the cell. The anterior part of a smaller daughter cell, referred to as cell C1, remains associated with the flagellum of maternal promastigote. C1 divides twice to give rise first to two equivalent cells (C2), and then to four morphologically similar cells (C3). C2 join with each other, and afterwards C3 attach between themselves as well via short cytoplasmic outgrowths, which appear instead flagella. In the point of outgrowth attachment of only one C2 and then of only one C3 to maternal flagellum zonal desmosomes occur. C1--C3 of L. oncopelti are similar to so-called straphangers (cyst-like parasites attached to the flagellum of maternal promastigote) known in some species of the genera Leptomonas and Blastocrithidia. Basal bodies are present in C1 and C2 but not in C3. DNA fibrils in the kinetoplast lack their common circular configuration, they progressively condense to form a disordered mass. C3 chromatin becomes denser to acquire eventually a characteristic "labyrinthine structure" looking like a huge bundle of whorled filaments 3-5 nm width. Inside this bundle there are channels of 10-12 nm in diameter filled with karyoplasm. On becoming ovoid, C3 are separated from the maternal promastigote flagellum and differentiate into mature "cysts". Straphangers C1--C3 and mature "cysts" lack any visible outer extracellular protective envelope (cyst wall). Instead, these cells have a cortical complex made of a reinforced plasmatic membrane underlined by a layer of a dense granular cytoplasm free of subpellicular microtubules. The mature "cyst" endoplasm shows a high electron density, and because of this identification of the majority of cellular organelles is next to impossible. Nevertheless, in both C3 and mature "cysts" some unusual membranes are seen composed of two electron lucent layers, with a single electron dense layer in between.

[Cryptobia udonellae sp. n. (Kinetoplastidea: Cryptobiida) - parasites of the excretory system of Udonella murmanica (Udonellida)]. / Cryptobia udonellae sp. n. (Kinetoplastidea: Cryptobiida) - parazit vydelitel'noi sistemy Udonella murmanica (Udonellida).

A new cryptobiid flagellates, Cryptobia udonellae sp. n., is described from the excretory channels of Udonella murmanica. The body of flagellates is spindle-shaped. The flagellar pocket is subapical. Two flagella emerge from the pocket. One flagellum turns anterior and is forward-directed; the other flagellum is directed posterior and close to the ventral cell surface. The ventral groove is well developed. The cytostome opens just anterior to the flagellar pocket. The cytostome leads to the short cytopharynx. In the excretory channel of worms the flagellates C. udonellae sp. n. are attached to microvilli of epithelium or lay free in the lumen. Both flagellates have been studied with TEM. The unusual parasite system which involves organisms of four different phylums of animals has been described for the first time.

[The phylogeny of the Trypanosomatidae: the molecular and morphological approaches]. / Filogeniia tripanosomatid: molekuliarnyi i morfologicheskii podkhody.

The results of comparative analysis of two phylogenetic trees of the trypanosomatids based on morphological and molecular characters are discussed. The morphological dendrogram was based on 33 ultrastructural characters, 6 light microscope characteristics and 8 biological characters. Molecular UPGMA dendrogram depicting differences (Dice distance) between examined trypanosomatids is based on the universally primed PCR polymorphisms. The general topology of both dendrograms are similar, with the Trypanosoma at the base. The genus Wallaceina appears to be monophyletic. In a contrary, the genera Leptomonas, Crithidia and Herpetomonas look like artificial groups according to both methods used. The cyst-forming homoxenous trypanosomatids from insects represent a monophyletic clade, which seems to be a separate genus. Two species of within genus Wallaceina are arranged as a separate subgenus.

[The taxonomic rank and place of Colpodellida in the system of the Protista]. / Taksonomicheskii rang i mesto v sisteme protistov Colpodellida.

The analysis of ultrastructure organisation and divergent processes in Colpodellida, Perkinsida, Gregarinea and Coccidea has confirmed the presence of unique basic structures in all of these organisms and the necessity to combine them into the single phylum Sporozoa. A taxonomic rank and place of Colpodellida in the system of living organisms is represented as follows: phylum Sporozoa Leuckart, 1879; em. Krylov, Mylnikov, 1986. (Syn.: Apicomplexa Levine, 1970). Predators or parasites. Common basic structure: pellicular membranes, subpellicular microtubules, micropores, conoid, rhoptries and micronemes, tubular mitochondrial cristae. Class Perkinsea Levine, 1978. Predators or parasites, vegetative stages with two heterodynamic flagella. Subclass 1. Colpodellia nom. nov. (Syn.: Spiromonadia Krylov, Mylnikov, 1986). Predators, two heterodynamic flagella with string-like mastigonemes (if present), division is exclusively within a cyst, with 2-4 daughter cells being produced, extrusomes are trichocyst-like. Subclass 2. Perkinsia Levine, 1978. Parasites, zoospores with two heterodynamic flagella, mastigonemes (if present) bristle-like or string-like.