Two myxosporean species, Zschokkella pleomorpha Lom et Dyková, 1995 (Zp) and Ortholinea fluviatilis Lom et Dyková, 1995 (Of) from the kidney of Tetraodon fluviatilis were studied by transmission electron microscope. Coelozoic sporogonie plasmodia of both species use pseudopodia-like projections for attachment to the epithelial cells of renal tubules. These projections either attach to host microvilli forming an interface reminiscent of septate junction (Zp) or are embedded into the epithelial cell surface (Of) or are inserted into gaps between epithelial cells (Zp, Of). Zp produces spores only by direct division of generative cells while in Of pansporoblasts prevail over direct division of generative cells. Sporogonie plasmodia of Zp greatly differ in size and in the variety of cytoplasmic constituents. A special feature in capsulogenesis is a transient envelope encasing the capsular primordium; there are fine fibres on the surface of the nascent filament spaced at 11 nm. In Of, vegetative nuclei of the plasmodium adhere to generative cells in a way reminding of sporoplasmic plasmodium of actinospores. In Of plasmodia, several unusual cytoplasmic structures were observed (membrane bound bodies with fuzzy radial contents or with a central dense inclusion, and endoplasmic reticulum cistemae forming a scalloped network). Of may also form intracellular coelozoic sporogonie plasmodia in the epithelial cells of renal tubules; these stages do not seem to constitute an important part of the life cycle.
Soricimyxum fegati gen. et sp. n. is a new myxosporean (Myxozoa) species discovered in the liver of shrews, Sorex araneus L., collected in the Bialowieza primeval forest (Poland). Both developmental stages and mature spores were found during a histological study. The infection had about 40% prevalence at the investigated locality. Plasmodia were polysporic. Elongated plasmodia with an average size of 30 by 8 µm occupied bile ducts and larger rounded plasmodia up to 80 µm in diameter were found in liver parenchyma where they most probably entered after the ducts had been destructed. Plasmodia in both locations elicited a vigorous inflammatory reaction. Spores were of an ovoid shape, 7 µm long, 5.4 µm wide and about 3.5 µm thick. They had two shell valves and two equal polar capsules, located in opposite ends of the spore.
Four strains of non-encysting amoebae were isolated from organs of freshwater fishes and characterized using light and electron microscope. Morphology of three clonal strains was consistent with amoebae which had already been described from water habitats. Two strains, one isolated from kidney tissue of common goldfish, Carassius auratus (Linnaeus, 1758), and the second one from brain of chub, Leuciscus cephalus Linnaeus, 1758, were identified with Vannella platypodia (Gläser, 1912) Page, 1976. Both strains were identical, except for the length of glycostyles. The strain isolated from the liver of perch, Perea fluviatilis (Linnaeus, 1758), was assigned to the genus Vexillifera Schaeffer, 1926 as Vexillifera expectata sp. n. The taxonomic position of the fourth non-encysting strain could not be safely established, although it shares some trophic cell structures with protostelids (Protostelia, Eumycetozoea). We present its detailed description here also to demonstrate that amoeba stages of this type of organisms are capable to infect fishes.