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| PHYLUM MICROSPORIDIOMYCOTA | |||||
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A. Spores of Chytridiopsis developing within the host nucleus. |
B. Living spores of Glugea with the coiled polar filament visible in some of the spores. |
C. A spore of Nosema with the polar filament everted. |
| Images taken from: A-C: http://www.biol.lu.se/cellorgbiol/microsporidia/9sm_chytridiopsis.jpg |
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The microsporidians are intracellular parasites of animals and protists. They are highly reduced in form and develop in intimate association with certain parts of cells or organelles (e.g. Chytridiopsis grows within the host nucleus; Figure A). They can be quite important, especially to those who raise bees and fish. Glugea (Figure B) attacks fish and makes large tumor-like cysts on their gills, bodies, and organs. Nosema (Figure C) can infect honeybee colonies, particularly in the spring and decimate them.
| The following description comes from Patterson (1999), Margulis and Schwartz (1998), Keeling (2002), Weiser (1985b), and Canning and Vavra (2000). |
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I. SYNONYMS: Microsporidians, myxosporidiomycota, cnidosporidians. II. NUMBER: >1,500 species III. PHYLUM CHARACTERISTICS A Structure and Physiology Cell Form: Unicellular spores enclosed by an imperforate wall within which one uninucleate or dinucleate sporoplasm is associated with and extrusion apparatus composed of a polar cap and an eversible polar filament. Amoeboid sporoplasm emerges from the polar tube when the spore "hatches," and this often develops into a syncytial plasmodium. For illustrated spore structure and life history see Glugea Spore Structure and Life History. Flagella: No flagella. Basal Bodies: Not known. Cell Covering: Spore wall of 3 layers. Chloroplasts: Not present. Food Reserves: Not known. Mitochondria: Not present. Nucleus: Diploid? Centrioles: Reported. Inclusions and Ejectile Organelles: Ejects polar filament from spore which resembles the nematocyst of the coelenterates. B. Mitosis, Meiosis and Life History Mitosis: Closed with an intranuclear spindle whose poles center on plaques (centrioles??). Meiosis: Suspected. Sexual Reproduction and Life History: For life history see Cell Form and the Glugea Spore Structure and Life History. C. Ecology: Parasites of animals and protists. |
Patterson (1999) identifies their defining synapomorphy as an introverted filament, and thus considers them to be a natural group. However, until recently their affinities were a mystery.
Generally, the microsporideans have been considered "sporozoans" (e.g. Grell 1973; and Kudo 1966). As recently as 1988, Margulis and Schwartz lumped the microsporidians and the myxozoans together in the phylum, Cnidosporidia (Pr-20), but they later separated them (Margulis and Schwartz 1998; Pr-2). Weiser (1985b) was one of the first students of the group to recognize their unique features and push to give them phylum-level status. Those who follow the Archezoa Hypothesis (e.g. Cavalier-Smith 1983; and Tudge 2000) consider them to be primitive and branch from the base of the Eukaryotic tree. However, recent evidence (Fast and Keeling 2001; Keeling 2002; Sokolova et al. 2003; and Ragan et al. 2003) places them squarely in the opisthokonts, allied with the fungi. Indeed, Keeling (2002) seems to show adequate evidence that the microsporidians are parasites that evolved from a zygomycete ancestor. The most recent taxonomic system for the microsporidians is that of Sprague et al. (1992), who proposed a complex scheme with three classes based entirely on morphology. Canning and Vavra (2000) back away from the use of all higher taxa within the phylum as do Adl et al. (2005). Thus, I will continue to use the more traditional morphological taxonomic system of Weiser (1985b) until a usable system confirmed by molecular evidence develops.
| TAXONOMY OF THE PHYLUM MICROSPOROMYCOTA. This system is an adaptation of Weiser (1985b). |
CLASS METCHNIKOVELLOMYCETES
CLASS MICROSPOROMYCETES
ORDER NOSEMALES
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This page is maintained by Jack R. Holt and Carlos A. Iudica. Last revised 03/12/2008.
