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The Myxozoa (etymology
Etymology

Etymology is the study of the roots and history of words; and how their form and meaning have changed over time.In languages with a long detailed history, etymology makes use of philology, the study of how words change from culture to culture over time....
: Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
: myx- "slime" or "mucus" + zoa "animals") are a group of parasitic animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
 and an annelid
Annelid

The annelids, collectively called Annelida , are a large Scientific classification of animals comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches....
 worm or bryozoa
Bryozoa

Bryozoans are tiny colonial animals that generally build stony skeletons of calcium carbonate, superficially similar to coral . Members of the Phylum Bryozoa are known as "moss animals" or "moss animacules" or as "sea mats"....
n. Infection occurs through valved spores. These contain one or two sporoblast cells and one or more polar capsules that contain filaments which anchor the spore to its host.






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The Myxozoa (etymology
Etymology

Etymology is the study of the roots and history of words; and how their form and meaning have changed over time.In languages with a long detailed history, etymology makes use of philology, the study of how words change from culture to culture over time....
: Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
: myx- "slime" or "mucus" + zoa "animals") are a group of parasitic animal
Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s of aquatic environments. Over 1300 species have been described and many have a two-host lifecycle, involving a fish
Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
 and an annelid
Annelid

The annelids, collectively called Annelida , are a large Scientific classification of animals comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches....
 worm or bryozoa
Bryozoa

Bryozoans are tiny colonial animals that generally build stony skeletons of calcium carbonate, superficially similar to coral . Members of the Phylum Bryozoa are known as "moss animals" or "moss animacules" or as "sea mats"....
n. Infection occurs through valved spores. These contain one or two sporoblast cells and one or more polar capsules that contain filaments which anchor the spore to its host. The sporoblasts are then released as a motile form, called an amoebula, which penetrates the host tissues and develops into one or more multinucleate
Multinucleate

Multinucleate cells have more than one Cell nucleus per Cell , which is the result of nuclear division not being followed by cytokinesis. As a consequence, multiple nuclei share one common cytoplasm....
 plasmodia. Certain nuclei later pair up, one engulfing another, to form new spores.

Phylogenetics


The Myxozoa were originally considered protozoa
Protozoa

Protozoan are microorganisms classified as unicellular eukaryotes. While there is no exact definition of the term "protozoan", most scientists use the word to refer to a unicellular heterotrophic protist, such as an amoeba or a ciliate....
n, and were included among other non-motile forms in the group Sporozoa. As their distinct nature became clear through 18S ribosomal DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 (rDNA) sequencing, they were relocated in the metazoa. Further classification was hindered by conflicting evidence: although 18S rDNA suggested an affinity with Cnidaria
Cnidaria

Cnidaria Cnidarians were for a long time grouped with Ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla....
, other rDNA sampled, and the HOX genes of two species, were more similar to those of the Bilateria
Bilateria

The Bilateria are all animals having a symmetry #Bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside....
.

The discovery that Buddenbrockia plumatellae
Buddenbrockia plumatellae

Buddenbrokia plumatellae is a parasitic worm whose taxonomic placement long puzzled biologists. It is now classified as one of the only two myxozoans of class Malacosporea on the basis of both genetic and ultrastructural studies....
, a worm-like parasite up to 2 mm in length (relatively large), is a myxozoan appeared to strengthen the case for a bilaterian origin, as the body plan is superficially similar. Nevertheless, closer examination reveals that Buddenbrockia is not longitudinally symmetrical by two ways, but four, casting doubt on this hypothesis
Hypothesis

A hypothesis consists either of a suggested explanation for an observable phenomenon or of a reasoned proposal predicting a possible causal correlation among multiple phenomena....
.

Further testing has sourced the first three HOX genes found in previous research (Myx1-3) to the bryozoan Cristatella mucedo, and the fourth (Myx4) to Northern pike
Northern Pike

The northern pike , Esox lucius, is a species of carnivorous fish of the genus Esox . They are typical of brackish water and freshwaters of the northern hemisphere ....
. This explained the confusion; original experiments had used contaminated tissue from host organisms, leading to false positives for a position among the Bilateria. More careful cloning of 50 coding genes from Buddenbrockia established the clade as severely modified members of the phylum Cnidaria
Cnidaria

Cnidaria Cnidarians were for a long time grouped with Ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla....
, with medusozoans as their closest relatives. Similarities between myxozoan polar capsules and cnidarian nematocysts (stinging cells) had been drawn for a long time, but were generally assumed to be the result of convergent evolution
Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action....
.

Taxonomists now recognize the outdated subgroup Actinosporea as a life-cycle
Biological life cycle

A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction....
 phase of Myxosporea
Myxosporea

The Myxosporea are a Class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish....
.

Species

Some species of myxozoa include:

  • Class Malacosporea
    • Buddenbrockia plumatellae
      Buddenbrockia plumatellae

      Buddenbrokia plumatellae is a parasitic worm whose taxonomic placement long puzzled biologists. It is now classified as one of the only two myxozoans of class Malacosporea on the basis of both genetic and ultrastructural studies....
    • Tetracapsuloides bryosalmonae
      Tetracapsuloides bryosalmonae

      Tetracapsuloides bryosalmonae is a myxozoan parasite of salmonid fishes, which causes Proliferative kidney disease , one of the most serious parasitic diseases of salmonid populations in Europe and North America, which causes losses of up to 90% in infected populations....
       - an important salmon
      Salmon

      Salmon is the common name for several species of fish of the family Salmonidae. Several other fish in the family are called trout,the difference is often attributed to the migratory life of the salmon as compared to the residential behaviour of trout, this holds true for the Atlantic salmon....
       parasite.
  • Class Myxosporea
    Myxosporea

    The Myxosporea are a Class of microscopic parasites, belonging to the Myxozoa. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate and an ectothermic vertebrate, usually a fish....
    • Myxobolus cerebralis
      Myxobolus cerebralis

      Myxobolus cerebralis is a myxosporean parasite of salmonidaes that causes whirling disease in fish farming salmon and trout and also in fish stocks....
       - an important parasite of salmon and trout
      Trout

      Trout are a number of species of freshwater fish belonging to the Salmoninae subfamily of the Salmonidae family. Salmon belong to some of the same genera as trout but, unlike most trout, most salmon species spend almost all their lives in salt water....
      .


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