has not officially changed. Recent molecular studies suggest they are related to Bilateria or Cnidaria, with Cnidaria being closer morphologically because both groups have extrusive filaments. Bilateria were somewhat closer in some genetic studies, but those were found to have used samples that were contaminated by material from the host organism, and a 2015 study confirms they are cnidarians. Taxonomy M. cerebralis is one of the 1,350 known myxozoan parasites known to infect fish. Once thought to be a species of Protozoa, taxonomists noticed characteristics that more closely related M. cerebralis to the phylum Cnidaria. These features included cnidocysts, which are tentacles that are used to hold onto and prey upon the host. M. cerebralis has many diverse stages ranging from single cells to relatively large spores, not all of which have been studied in detail. This complex lifecycle involves two different hosts and numerous developmental stages. These stages happen through mitosis, endogeny, plasmotoney, or possibly meisos. In the first part of its lifecycle, M. cerebralis is attached to its salmonid host externally. They then use their stinging tentacles to infect the host, causing the skeletal tissues and nervous system become deformed. Today, the myxozoans, previously thought to be multicellular protozoans, are considered animals by most scientists, though their status has not officially changed. Recent molecular studies suggest they are related to Bilateria or Cnidaria, with Cnidaria being closer morphologically because both groups have extrusive filaments. Bilateria were somewhat closer in some genetic studies, but those were found to have used samples that were contaminated by material from the host organism, and a 2015 study confirms they are cnidarians. Morphology M. cerebralis has many diverse stages ranging from single cells to relatively large spores, not all of which have been studied in detail. Triactinomyxon stage The stages that infect fish, called triactinomyxon spores, are made of a single style that is about 150 micrometers (μm) long and three processes or "tails", each about 200 micrometers long. These spores are typically oval shaped, and display asymmetrical symmetry. A sporoplasm packet at the end of the style contains 64 germ cells surrounded by a cellular envelope. There are also three polar capsules, each of which contains a coiled polar filament between 170 and 180 μm long, with about 5-6 coils in each filament. Polar filaments in both this stage and in the myxospore stage (see picture above) rapidly shoot into the body