Myxozoa

Article By:

Fiala, Ivan Faculty of Biological Sciences, University of South Bohemia, České Budějovice, Czech Republic.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.900157

A phylum of metazoan parasites exhibiting an extremely reduced body size and structure during their evolution. Myxozoans form only plasmodial vegetative stages that produce spores, which are the source of infection. The only exception is the malacosporean Buddenbrockia plumatellae, which lives in bryozoans and involves a macroscopic wormlike stage in its life cycle. Myxozoan spores consist of several cells, which are transformed into shell valves, ameboid infectious germ cells, and nematocyst-like polar capsules with coiled extrudable polar filaments. Typically, two morphologically different types of spores are developed: myxospores (Fig. 1) in the intermediate vertebrate host and actinospores in the definitive (final) annelid host. For the majority of their known history, myxozoans were considered to be protists. However, phylogenetic analysis of myxozoan molecular data confirmed their close relationship to metazoans. Further analysis of several protein-coding genes has suggested a close relationship with Cnidaria. Few of the more than 2000 myxozoan species are severe pathogens of fish, which are their typical vertebrate hosts. See also: Cnidaria; Metazoa; Parasitology

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