Myxosporea

Myxopsporean species are microscopic parasites. They have a "double life". The complex life cycle comprise vegetative forms in two hosts, an aquatic invertebrate (generally an annelid) and an aquatic vertebrate (generally a fish). Each host release a different type of spores so different that until recent they were being treated as different parasites.

The myxosporean species are identified generally by the size and shape of the spores released by vertebrate hosts. For instance, the genus Ceratomyxa is a very frequent parasite of the gallbladder of many fish species; they have "boomerang like" spores with 2 polar capsules resembling eyes in the middle of the spore. The size of this spores generally range between 15 and 100 micrometers in most Ceratomyxa species. Other genuses have round or oval spores with only one polar capsules or with more than two.

Examples of Myxosporean genuses are Kudoa, destroying the muscle of fishes, Myxobolum from freshwater fish heart, Myxidium, Sphaerospora or Henneguya. The second type of spores resemble three or four hooks united by the base, are released generally by an annelid host and can also be used for identification. Some myxosporeans cause important diseases in cultured fishes, for instance the kidney disease named PDK in salmonids.