A list of myxozoan genera is presented in the current taxonomical scheme. These genera are defined; their type species and most important pathogens along with their hosts are listed. Simultaneously, definitions of actinospore stages representing sexual stages of the myxosporean life cycle are given; altogether, 17 actinospore collective groups with 180 types have been described. Life cycles of the two classes of the phylum Myxozoa, Malacosporea and Myxosporea, are briefly outlined with specification of the appropriate terms. Up to now, 4 malacosporean and 2,180 myxosporean species assigned to a total of 62 genera, have been established. The surviving classification of myxosporeans, based on spore morphology, is discussed in the context of the still fragmentary data resulting from SSU rDNA sequence analyses. The main task for the future is a rigorous, detailed morphological description combined with molecular techniques in establishment of new species and in revision of the existing ones. Establishment of a classification acceptable from morphological, biological and phylogenetical viewpoints is necessary.
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.