Myxozoa

The Myxozoa aregroupmicroscopic, parasitic animals. Originallywere considered protozoa,includedother non-motile forms ingroup Sporozoa. However, as their distinct nature became clearwere removedtheir own phylum. Theynow generally consideredhave developed from multicellular animals, andclassifiedthem.

Many Myxozoa havetwo-host lifecycle, involvingfishan annelid worm or bryozoan. Infection occurs by valved spores. These contain one or two sporoblast cells,one or more polar capsules, containing filaments that anchorssporeits host. The sporoblaststhen released asmotile form called an amoebula, which penetrateshost tissuesdevelops into one or more multinucleate plasmodia. Certain nuclei later pair up, one engulfing another,form new spores.

The polar capsulesvery similarstructureappearance tostinging cellsCnidaria. On accountthisMyxozoa have been generally heldbe extremely reduced cnidarians,in particular have been considered close relativesPolypodium,some genetic support. More recent studiesHox genes, however, pointan origin amongBilateria. This has been given strong support bydiscovery that Buddenbrockia,worm-like parasitebryozoans up2 mmlength, belongs amongMyxozoa. Genetically italmost indistinguishable fromother forms,it has Myxozoan-like spore capsules, butretainsbilateral body formlongitudinal muscles. This serves asmissing link betweenMyxozoatheir multicellular ancestors.

Myxozoasplit into two classes, MalacosporeaMyxosporea. The outdated subgroup Actinosporeanow recognized aslife cycle phaseMyxosporea.

Some species:

• Class Malacosporea
  • Buddenbrockia plumatellae
  • Tetracapsuloides bryosalmonae, an important parasitesalmon
• Class Myxosporea

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