Class MYXOZOA Grasse, 1970

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Introduction

Myxozoans produce multicellular spores comprised of valvogenic cells forming spore shell valves, sporoplasmic cells acting as infective germ cells, and capsulogenic cells forming polar capsules with extrudible filaments (similar to cnidarian nematocysts — but used for attachment rather than hunting or defence). Some 3,000 myxozoan species have been described, most as coelozoic or histozoic parasites in the organ cavities and tissues of fish although some are found in amphibia, reptiles and various invertebrates (especially oligochaetes, polychaetes and sipunculids). The life cycles of several species (mainly from freshwater fishes) have been found recently to involve cyclic development between myxosporean stages in fishes and actinosporean stages in invertebrates. The Myxozoa were originally thought to have affinities with the Microspora which form unicellular spores, so many early classification schemes placed them together in the subkingdom Protozoa (Protista, Protoctista). However, ultrastructural and molecular studies indicate that the Myxozoa are bilateral metazoans and they have been transferred to the Animalia (Holozoa, Metazoa) in the supergroup Opisthokonta. For taxonomic considerations, see Adl et al. (2012).

General References

Adl, S.M., Simpson, A.G.B., Lane, C.E., Lukes, J., Bass, D., Bowser, S.S., Brown, M.W., Burki, F., Dunthorn, M., Hampl, V., Heiss, A., Hoppenrath, M., Lara, E., Le Gall, L., Lynn, D.H., McManus, H., Mitchell, E.A.D., Mozley-Stanridge, S.E., Parfrey, L.W., Pawlowski, J., Rueckert, S., Shadwick, L., Schoch, C.L., Smirnov, A. & Spiegel, F.W. 2012. The revised classification of eukaryotes. Journal of Eukaryotic Microbiology 59: 429-493

History of changes