myxozoa

Myxozoans are endoparasitic animals exhibiting complex life cycles that, in most of the documented cases, involve an intermediate host, usually a fish, but in rare cases amphibians,{{cite journal |author=Eiras, Jorge C. |year=2005 |title=An overview on the myxosporean parasites in amphibians and reptiles |url=http://www.actaparasitologica.pan.pl/archive/PDF/Eiras.pdf |journal=Acta Parasitologica |volume=50 |issue=4 |pages=267–275 |issn=1230-2821}} reptiles, birds,{{cite journal |author1=Bartholomew, J.L. |author2=Atkinson S.D. |author3=Hallett, S.L. |author4=Lowenstine, L.J. |author5=Garner, M.M. |author6=Gardiner, C.H. |author7=Rideout, B.A. |author8=Keel, M.K. |author9=Brown, J.D. |year=2008 |title=Myxozoan parasitism in waterfowl |journal=International Journal for Parasitology |volume=38 |issue=10 |pages=1199–1207 |pmid=18342316 |doi=10.1016/j.ijpara.2008.01.008 |url=https://www.researchgate.net/publication/5510638}} and mammals;{{cite journal |author1=Prunescu, Carol-Constantin |author2=Prunescu, Paula |author3=Lom, Jiří |year=2007 |title=The first finding of myxosporean development from plasmodia to spores in terrestrial mammals: Soricimyxum fegati gen. et sp. n. (Myxozoa) from Sorex araneus (Soricomorpha) |journal=Folia Parasitologica |volume=54 |issue=3 |pages=159–164 |doi=10.14411/fp.2007.022 |pmid=19245186|s2cid=45278079 |doi-access=free }}{{cite journal |author1=Székely, Csaba |author2=Cech,Gábor |author3=Atkinson, Stephen D. |author4=Kálmán Molnár |author5=Egyed, László |author6=Gubányi, András |year=2015 |title=A novel myxozoan parasite of terrestrial mammals: Description of Soricimyxum minuti sp. n. (Myxosporea) in pygmy shrew Sorex minutus from Hungary |journal=Folia Parasitologica |volume=62 |issue=1 |pages=45–49 |doi=10.14411/fp.2015.045 |doi-access=free |pmid=26370293 |url=http://real.mtak.hu/45474/1/Folia2015Soricimyxumminuti.pdf}} and a definitive host, usually an annelid or an ectoproct.

Image:Myxozoans_Life_Cycle.jpg

Only about 100 life cycles have been resolved and it is suspected that there may be some exclusively terrestrial.{{cite book |author1=Hallett, Sascha L. |author2=Bartholomew, Jerri L. |author3=Atkinson, Stephen D. |author4=Székely, Csaba |year=2015 |chapter=Myxozoans exploiting homeotherms |editor=Okamura, B. |editor2=Gruhl, A. |editor3=Bartholomew, J.L. |title=Myxozoan Evolution, Ecology, and Development |pages=125–138 |publisher=Springer International Publishing |doi=10.1007/978-3-319-14753-6_7 |isbn=978-3-319-14752-9 |s2cid=83229156 |chapter-url=https://www.researchgate.net/publication/275024260}} The mechanism of infection occurs through valve spores{{what|date=March 2023}} that have many forms, but their main morphology is the same: one or two sporoplasts, which are the real infectious agent, surrounded by a layer of flattened cells called valve cells, which can secrete a layer protective coating and form float appendages. Integrated into the layer of valve cells are two to four specialized capsulogenic cells (in a few cases, one or even 15), each carrying a polar capsule containing coiled polar filaments, an extrudable organelle used for recognition, contact and infiltration.{{cite book |last=Gruhl |first=Alexander |year=2015 |chapter=Chapter 7 - Myxozoa |editor-last=Wanninger |editor-first=Andreas |title=Evolutionary developmental biology of invertebrates |volume=1: Introduction, non-bilateria, acoelomorpha, xenoturbellida, chaetognatha |pages=165–177 |publisher=Springer Verlag Wien |isbn=978-3-7091-1861-0 |doi=10.1007/978-3-7091-1862-7_7 |chapter-url=https://www.researchgate.net/publication/282249669}} Myxospores are ingested by annelids, in which the polar filaments extrude to anchor the spore to the gut epithelium. Opening of the shell valves allows the sporoplasms to penetrate into the epithelium. Subsequently, the parasite undergoes reproduction and development in the gut tissue, and finally produces usually eight actinosporean spore stages (actinospores) within a pansporocyst. After mature actinospores are released from their hosts they float in the water column.{{cite journal |author1=el Matbouli, M. |author2=Hoffmann, R.W. |year=1998 |title=Light and electron microscopic studies on the chronological development of Myxobolus cerebralis to the actinosporean stage in Tubifex tubifex |journal=International Journal for Parasitology |volume=28 |issue=1 |pages=195–217 |doi=10.1016/s0020-7519(97)00176-8 |pmid=9504346 |url=https://www.researchgate.net/publication/51301823}} Upon contact with skin or gills of fish, sporoplasms penetrate through the epithelium, followed by development of the myxosporean stage. Myxosporean trophozoites are characterized by cell-in-cell state, where the secondary (daughter) cells develop in the mother (primary) cells. The presporogonic stages multiply, migrate via nervous or circulatory systems, and develop into sporogonic stages. At the final site of infection, they produce mature spores within mono- or di-sporic pseudoplasmodia, or poly-sporic plasmodia.{{cite journal |author1=el Matbouli, M. |author2=Hoffmann, R.W. |author3=Mandok, C. |year=1995 |title=Light and electron microscopic observations on the route of the triactinomyxon-sporoplasm of Myxobolus cerebralis from epidermis into rainbow trout (Oncorhynchus mykiss) cartilage |journal=Journal of Fish Biology |volume=46 |issue=6 |pages=919–935 |doi=10.1111/j.1095-8649.1995.tb01397.x |url=https://www.researchgate.net/publication/227902174}}

Relationships between myxosporeans and their hosts are often highly evolved and do not usually result in severe diseases of the natural host. Infection in fish hosts can be extremely long-lasting, potentially persisting for the lifetime of the host. However, an increasing number of myxosporeans have become{{when|date=March 2023}} pathogens with significant impact to the commercial fish industry, largely as a result of aquaculture bringing new species into contact with myxosporeans to which they had not been previously exposed, and to which they are highly susceptible. The economic impact of such parasites can be severe, especially where prevalence rates are high; they may also have a severe impact on wild fish stocks.

The diseases caused by myxosporeas in cultured fish with the most significant economic impact worldwide are proliferative kidney disease (PKD) caused by the malacosporean T. bryosalmonae, and whirling disease, caused by a myxosporean M. cerebralis; both diseases affect salmon. Enteromyxosis is caused by E. leei in cultured marine sparids, while proliferative gill disease (or “hamburger disease”) is caused by H. ictaluri in catfish and S. renicola infections occur in common carp.

Myxozoans are very small animals, typically 10–300 μm in length.{{cite book |last1=Canning |first1=Elizabeth U. |last2=Okamura |first2=Beth |chapter=Biodiversity and Evolution of the Myxozoa |date=2003-01-01 |title=Advances in Parasitology |volume=56 |pages=43–131 |publisher=Academic Press |language=en |doi=10.1016/S0065-308X(03)56002-X |pmid=14710996 |isbn=978-0-12-031756-1}}

Like other cnidarians they possess cnidocysts, which were referred to as "polar capsules" before the discovery that myxozoans are cnidarians. These cnidocysts fire tubules as in other cnidarians; some inject substances into the host. However, the tubules lack hooks or barbs, and in some species are more elastic than in other cnidarians.

Myxozoans have secondarily lost epithelial structures, a nervous system, gut, and cilia. Most lack muscles, though these are retained in some members of malacosporea. Those who have lost their muscles move around inside the host using other forms of locomotion, such as the use of filopodia, spore valve contractions, amoeboid movements, and rapidly creating and reabsorbing folds on the cell membrane.{{cite journal |last1=Hartigan |first1=A. |last2=Estensoro |first2=I. |last3=Vancová |first3=M. |last4=Bílý |first4=T. |last5=Patra |first5=S. |last6=Eszterbauer |first6=E. |last7=Holzer |first7=A. S. |title=New cell motility model observed in parasitic cnidarian Sphaerospora molnari (Myxozoa:Myxosporea) blood stages in fish |journal=Scientific Reports |date=16 December 2016 |volume=6 |issue=1 |pages=39093 |doi=10.1038/srep39093 |doi-access=free |pmc=5159882 |pmid=27982057|bibcode=2016NatSR...639093H }} Myxozoans do not undergo embryogenesis during development and have lost true gametes. Instead, they reproduce via multicellular spores. These spores contain the polar capsules, which are not typically present in somatic cells. Centrioles are not involved in the nuclear division of myxozoans. Cell division by binary fission is rare, and cells divide instead via endogeny.

In 2020, the myxozoan Henneguya salminicola was found to lack a mitochondrial genome, and thus be incapable of aerobic respiration; it was the first animal to be positively identified as such. Its actual metabolism is currently unknown.{{cite journal |last1=Yahalomi |first1=Dayana |last2=Atkinson |first2=Stephen D. |last3=Neuhof |first3=Moran |last4=Chang |first4=E. Sally |last5=Philippe |first5=Hervé |last6=Cartwright |first6=Paulyn |last7=Bartholomew |first7=Jerri L. |last8=Huchon |first8=Dorothée |date=2020-03-10 |title=A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=10 |pages=5358–5363 |doi=10.1073/pnas.1909907117 |doi-access=free |issn=0027-8424 |pmid=32094163 |pmc=7071853 |bibcode=2020PNAS..117.5358Y |language=en }}

Myxozoans were originally considered to be protozoans,

{{cite journal

|author=Štolc, A.

|title=Actinomyxidies, nouveau groupe de Mesozoaires parent des Myxosporidies

|year=1899

|journal= Bull. Int. l'Acad. Sci. Bohème

|volume=12

|pages=1–12}}

and were included among other non-motile forms in the group Sporozoa.[https://web.archive.org/web/20081216220815/http://home.um.edu.mt/biology/phylogenetic%20classification.pdf Edwin Lanfranco, 2007, A phylogenetic classification of organisms other than animals]. As their distinct nature became clear through 18S ribosomal DNA (rDNA) sequencing, they were relocated in the metazoa. Detailed classification within the metazoa was however long hindered by conflicting rDNA evidence: although 18S rDNA suggested an affinity with Cnidaria,

{{cite journal

|author=Smothers, J.F.|date=September 1994

|title=Molecular evidence that the myxozoan protists are metazoans

|journal=Science

|volume=265

|issue=5179

|pages=1719–1721

|doi=10.1126/science.8085160

|pmid=8085160|display-authors=etal|bibcode=1994Sci...265.1719S

}}

other rDNA sampled,

{{cite journal

|author=A.S. Monteiro|title=Orphan worm finds a home: Buddenbrockia is a Myxozoan

|journal=Mol. Biol. Evol.

|volume=19

|issue=6

|pages=968–71

|pmid=12032254

|date= June 1, 2002

|doi=10.1093/oxfordjournals.molbev.a004155|display-authors=etal|doi-access=free

}}

{{cite journal

|author=J. Zrzavy & V. Hypsa

|date=April 2003

|title= Myxozoa, Polypodium, and the origin of the Bilateria: The phylogenetic position of "Endocnidozoa" in light of the rediscovery of Buddenbrockia

|journal=Cladistics

|volume=19

|issue=2

|pages=164–169

|doi=10.1111/j.1096-0031.2003.tb00305.x|bibcode=2002clad.book.....S

|s2cid=221583517

}}

and the HOX genes of two species,

{{cite journal

|author=C. L. Anderson, E. U. Canning & B. Okamura

|date=March 1999

|title=A triploblast origin for Myxozoa?

|journal=Nature

|pmid=9537319

|volume=392

|issue=6674

|pages=346–347

|doi=10.1038/32801|bibcode=1998Natur.392..346A

|s2cid=4426181

}}

were more similar to those of the Bilateria.

The discovery that Buddenbrockia plumatellae, a worm-like parasite of bryozoans up to 2 mm in length, is a myxozoan initially appeared to strengthen the case for a bilaterian origin, as the body plan is superficially similar. Nevertheless, closer examination reveals that Buddenbrockia{{'s}} longitudinal symmetry is not twofold, but fourfold, casting doubt on this hypothesis.

Further testing resolved the genetic conundrum by sourcing the first three previously identified discrepant HOX genes (Myx1-3) to the bryozoan Cristatella mucedo and the fourth (Myx4) to northern pike, the respective hosts of the two corresponding Myxozoa samples.

{{cite journal|author=E. Jímenez-Guri|display-authors=etal|date=July 2007|title=Buddenbrockia is a cnidarian worm|journal=Science|volume=317|issue=116|pages=116–118|bibcode=2007Sci...317..116J|doi=10.1126/science.1142024|pmid=17615357|s2cid=5170702}} This explained the confusion: the original experiments had used samples contaminated by tissue from host organisms, leading to false positives for a position among the Bilateria. More careful cloning of 50 coding genes from Buddenbrockia firmly established the clade as severely modified members of the phylum Cnidaria, with medusozoans as their closest relatives. Similarities between myxozoan polar capsules and cnidarian nematocysts had been drawn for a long time, but were generally assumed to be the result of convergent evolution.

Taxonomists now recognize the outdated subgroup Actinosporea as a life-cycle phase of Myxosporea.{{cite journal |author=Kent M. L. |author2=Margolis L. |author3=Corliss J.O. | year = 1994 | title = The demise of a class of protists: taxonomic and nomenclatural revisions proposed for the protist phylum Myxozoa Grasse, 1970 | journal = Canadian Journal of Zoology | volume = 72 | issue = 5| pages = 932–937 | doi=10.1139/z94-126|bibcode=1994CaJZ...72..932K }}

Molecular clocks suggest that myxozoans and their closest relatives, the polypodiozoa, shared their last common ancestor with medusazoans about 600 million years ago, during the Ediacaran period.

Myxozoan taxonomy has undergone great and important changes in its levels of generic, family and suborder classification. Fiala et al. (2015) proposed a new classification based on spores.{{cite book

| last1= Fiala | first1= Ivan

| last2= Bartošová-Sojková | first2= Pavla

| last3= Whipps | first3= Christopher M.

| year= 2015

| chapter = Classification and Phylogenetics of Myxozoa

| editor1-first= Beth | editor1-last= Okamura

| editor2-first= Alexander | editor2-last= Gruhl

| editor3-first= Jerri L. | editor3-last= Bartholomew

| title=Myxozoan Evolution, Ecology, and Development |pages=85–110

| publisher= Springer International Publishing

| isbn=978-3-319-14752-9 | doi=10.1007/978-3-319-14753-6_5

| chapter-url=https://www.researchgate.net/publication/275220745

}}

{{clade

|label1= 
  Phylum: Cnidaria

|1={{clade

|label1=  Subphylum: Myxozoa

|1={{clade

|label1=  Class: Malacosporea

|1={{clade

|label1= Order:Malacovalvulida

|1={{clade

|label1= Family:Saccosporidae

|1= Genus: Buddenbrockia, Tetracapsuloides

}}

}}

|label2=  Class: Myxosporea

|2={{clade

|label1= Order:Bivalvulida

|1={{clade

|label1= Suborder:Variisporina

|1={{clade

|label1= Family:Sphaeromyxidae

|1=Genus: Sphaeromyxa

|label2= Family:Myxidiidae

|2= Genus:
Myxidium, Zschokkella, Enteromyxum, Sigmomyxa, Soricimyxum, Cystodiscus

|label3= Family:Ortholineidae

|3= Genus:
Ortholinea, Neomyxobolus, Cardimyxobolus, Triangula, Kentmoseria

|label4= Family:Sinuolineidae

|4= Genus:
Sinuolinea, Myxodavisia, Myxoproteus, Bipteria, Paramyxoproteus, Neobipteria, Schulmania, Noblea, Latyspora

|label5= Family:Fabesporidae

|5= Genus: Fabespora

|label6= Family:Ceratomyxidae

|6= Genus:
Ceratomyxa, Meglitschia, Ellipsomyxa, Ceratonova

|label7= Family:Sphaerosporidae

|7= Genus:
Sphaerospora, Wardia, Palliatus

|label8= Family:Myxobilatidae

|8= Genus:
Myxobilatus, Acauda, Hoferellus

|label9= Family:Chloromyxidae

|9= Genus:
Chloromyxum, Caudomyxum, Agarella

|label10= Family:Coccomyxidae

|10= Genus:
Coccomyxa, Auerbachia, Globospora

|label11= Family:Alatosporidae

|11= Genus:
Alatospora, Pseudalatospora, Renispora

|label12= Family:Parvicapsulidae

|12= Genus:
Parvicapsula, Neoparvicapsula, Gadimyxa

}}

|label2= Suborder:Platysporina

|2={{clade

|label1= Family:Myxobolidae

|1= Genus:
Myxobolus, Spirosuturia, Unicauda, Dicauda, Phlogospora, Laterocaudata, Henneguya, Hennegoides, Tetrauronema, Thelohanellus, Neothelohanellus, Neohenneguya, Trigonosporus

}}

}}

|label2= Order:Multivalvulida

|2={{clade

|label1= Family:Trilosporidae

|1= Genus: Trilospora, Unicapsula

|label2= Family:Kudoidae

|2= Genus: Kudoa

|label3= Family:Spinavaculidae

|3= Genus: Octospina

|4= incertae sedis:     Trilosporoides

}}

}}

}}

|label2=other Cnidarians

|2=  . . .   

}}

}}

• Smallest organisms

{{reflist|22em}}

{{Commons category|Myxozoa}}

• {{cite web |title=Myxozoa |website=Tree of Life |url=http://tolweb.org/Myxozoa/2460}}
• {{cite web |title=Myxozoan researchers network |type=main page |url=http://www.myxozoa.org/}}

{{Cnidaria}}

{{Taxonbar|from=Q134882}}

{{Authority control}}

Category:Animal classes