Myxozoa(etymology:Greek:μύξαmyxa"slime" or "mucus"[1]+ thematic vowel o + ζῷονzoon"animal"[2]) is a subphylum of aquaticcnidariananimals– all obligateparasites.It contains thesmallest animalsever known to have lived. Over 2,180 species have been described and some estimates have suggested at least 30,000 undiscovered species.[3]Many have a two-host lifecycle, involving afishand anannelidworm or abryozoan.The average size of amyxosporeansporeusually ranges from 10 μm to 20 μm,[4]whereas that of a malacosporean (a subclade of the Myxozoa) spore can be up to 2 mm. Myxozoans can live in both freshwater and marine habitats.
| Myxozoa | |
|---|---|
| |
| Triactinomyxon stage ofMyxobolus cerebralis | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Cnidaria |
| Subphylum: | Myxozoa Grassé,2021 |
| Classes | |
Myxozoans are highlyderivedcnidariansthat have undergone dramaticevolutionfrom a free swimming, self-sufficientjellyfish-like creature into their current form ofobligate parasitescomposed of very fewcells– sometimes only a single cell[citation needed].As myxozoans evolved into microscopic parasites, they lost manygenesresponsible for multicellular development, coordination,cell–cell communication,and even, in some cases,aerobic respiration.The genomes of some myxozoans are now among the smallest genomes of any known animal species.[5][6]
Life cycle and pathology
editMyxozoans are endoparasitic animals exhibiting complex life cycles that, in most of the documented cases, involve anintermediate host,usually a fish, but in rare cases amphibians,[7]reptiles,[7]birds,[8]and mammals;[9][10]and a definitive host, usually anannelidor anectoproct.
Only about 100 life cycles have been resolved and it is suspected that there may be some exclusively terrestrial.[11]The mechanism of infection occurs throughvalve spores[clarification needed]that have many forms, but their main morphology is the same: one or twosporoplasts,which are the real infectious agent, surrounded by a layer of flattened cells calledvalve cells,which can secrete a layer protective coating and formfloat appendages.Integrated into the layer of valve cells are two to four specializedcapsulogeniccells (in a few cases, one or even 15), each carrying apolar capsulecontaining coiledpolar filaments,an extrudable organelle used for recognition, contact and infiltration.[12]Myxospores are ingested by annelids, in which the polar filaments extrude to anchor the spore to the gutepithelium.Opening of the shell valves allows thesporoplasmsto 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 apansporocyst.After mature actinospores are released from their hosts they float in the water column.[13]Upon contact with skin or gills of fish, sporoplasms penetrate through the epithelium, followed by development of the myxosporean stage. Myxosporeantrophozoitesare 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-sporicpseudoplasmodia,or poly-sporicplasmodia.[14]
Relationships between myxosporeans and their hosts are often highly evolved and do not usually result in severe diseases of the natural host. Infection infishhosts can be extremely long-lasting, potentially persisting for the lifetime of the host. However, an increasing number of myxosporeans have become[when?]pathogens with significant impact to the commercial fish industry, largely as a result ofaquaculturebringing 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 suchparasitescan be severe, especially whereprevalencerates 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 areproliferative kidney disease(PKD) caused by themalacosporeanT. bryosalmonae,andwhirling disease,caused by amyxosporeanM. cerebralis;both diseases affectsalmon.Enteromyxosisis caused byE. leeiin cultured marinesparids,whileproliferative gill disease(or “hamburger disease” ) is caused byH. ictaluriincatfishandS. renicolainfections occur incommon carp.
Anatomy
editMyxozoans are very small animals, typically 10–300μmin length.[15]
Like other cnidarians they possesscnidocysts,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 lostepithelialstructures, anervous system,gut,andcilia.Most lackmuscles,though these are retained in some members ofmalacosporea.Those who have lost their muscles move around inside the host using other forms of locomotion, such as the use offilopodia,spore valve contractions, amoeboid movements, and rapidly creating and reabsorbing folds on the cell membrane.[16]Myxozoans do not undergo embryogenesis during development and have lost truegametes.[3]Instead, they reproduce via multicellular spores. These spores contain the polar capsules, which are not typically present in somatic cells.Centriolesare not involved in the nuclear division of myxozoans. Cell division bybinary fissionis rare, and cells divide instead viaendogeny.[15]
In 2020, the myxozoanHenneguya salminicolawas found to lack amitochondrialgenome,and thus be incapable ofaerobic respiration;it was the first animal to be positively identified as such. Its actual metabolism is currently unknown.[17]
Phylogenetics
editMyxozoans were originally considered to beprotozoans,[18]and were included among other non-motile forms in the groupSporozoa.[19]As their distinct nature became clear through 18SribosomalDNA(rDNA) sequencing, they were relocated in themetazoa.Detailed classification within the metazoa was however long hindered by conflicting rDNA evidence: although 18S rDNA suggested an affinity withCnidaria,[20]other rDNA sampled,[21][22]and theHOXgenes of two species,[23]were more similar to those of theBilateria.
The discovery thatBuddenbrockia plumatellae,a worm-like parasite ofbryozoansup to 2 mm in length, is a myxozoan[21]initially appeared to strengthen the case for a bilaterian origin, as the body plan is superficially similar. Nevertheless, closer examination reveals thatBuddenbrockia'slongitudinal symmetry is not twofold, but fourfold, casting doubt on thishypothesis.
Further testing resolved the genetic conundrum by sourcing the first three previously identified discrepant HOX genes (Myx1-3) to thebryozoanCristatella mucedoand the fourth (Myx4) tonorthern pike,the respective hosts of the two corresponding Myxozoa samples.[24]This explained the confusion: the original experiments had used samples contaminated by tissue from host organisms, leading tofalse positivesfor a position among the Bilateria. More careful cloning of 50 coding genes fromBuddenbrockiafirmly established the clade as severely modified members of the phylumCnidaria,withmedusozoansas their closest relatives.[24]Similarities between myxozoan polar capsules and cnidariannematocystshad been drawn for a long time, but were generally assumed to be the result ofconvergent evolution.
Taxonomists now recognize the outdated subgroup Actinosporea as alife-cyclephase ofMyxosporea.[25]
Molecular clocks suggest that myxozoans and their closest relatives, thepolypodiozoa,shared their last common ancestor withmedusazoansabout 600 million years ago, during theEdiacaranperiod.[3]
Taxonomy
editMyxozoan 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.[26]
Phylum: Cnidaria |
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See also
editReferences
edit- ^μύξα.Liddell, Henry George;Scott, Robert;A Greek–English Lexiconat thePerseus Project
- ^ζῷον.Liddell, Henry George;Scott, Robert;A Greek–English Lexiconat thePerseus Project
- ^abcAtkinson, Stephen D.; Bartholomew, Jerri L.; Lotan, Tamar (1 August 2018)."Myxozoans: Ancient metazoan parasites find a home in phylum Cnidaria".Zoology.129:66–68.Bibcode:2018Zool..129...66A.doi:10.1016/j.zool.2018.06.005.ISSN0944-2006.PMID30170750.S2CID52141614.
- ^Fiala, Ivan (10 July 2008)."Myxozoa".tolweb.org(under construction). The Tree of Life Web Project.
- ^Chang, E. Sally; Neuhof, Moran; Rubinstein, Nimrod D.; Diamant, Arik; Philippe, Hervé; Huchon, Dorothée; Cartwright, Paulyn (1 December 2015)."Genomic insights into the evolutionary origin of Myxozoa within Cnidaria".Proceedings of the National Academy of Sciences.112(48): 14912–14917.Bibcode:2015PNAS..11214912C.doi:10.1073/pnas.1511468112.ISSN1091-6490.PMC4672818.PMID26627241.
- ^Yahalomi, D.; Atkinson, S.D.; Neuhof, M.; Chang, E.S.; Philippe, H.; Cartwright, P.; Bartholomew, J.L.; Huchon, D. (24 February 2020)."A cnidarian parasite of salmon (Myxozoa:Henneguya) lacks a mitochondrial genome ".Proceedings of the National Academy of Sciences.117(10): 5358–5363.Bibcode:2020PNAS..117.5358Y.doi:10.1073/pnas.1909907117.PMC7071853.PMID32094163.
- ^abEiras, Jorge C. (2005)."An overview on the myxosporean parasites in amphibians and reptiles"(PDF).Acta Parasitologica.50(4): 267–275.ISSN1230-2821.
- ^Bartholomew, J.L.; Atkinson S.D.; Hallett, S.L.; Lowenstine, L.J.; Garner, M.M.; Gardiner, C.H.; Rideout, B.A.; Keel, M.K.; Brown, J.D. (2008)."Myxozoan parasitism in waterfowl".International Journal for Parasitology.38(10): 1199–1207.doi:10.1016/j.ijpara.2008.01.008.PMID18342316.
- ^Prunescu, Carol-Constantin; Prunescu, Paula; Lom, Jiří (2007)."The first finding of myxosporean development from plasmodia to spores in terrestrial mammals:Soricimyxum fegatigen. et sp. n. (Myxozoa) fromSorex araneus(Soricomorpha) ".Folia Parasitologica.54(3): 159–164.doi:10.14411/fp.2007.022.PMID19245186.S2CID45278079.
- ^Székely, Csaba; Cech,Gábor; Atkinson, Stephen D.; Kálmán Molnár; Egyed, László; Gubányi, András (2015)."A novel myxozoan parasite of terrestrial mammals: Description ofSoricimyxum minutisp. n. (Myxosporea) in pygmy shrewSorex minutusfrom Hungary "(PDF).Folia Parasitologica.62(1): 45–49.doi:10.14411/fp.2015.045.PMID26370293.
- ^Hallett, Sascha L.; Bartholomew, Jerri L.; Atkinson, Stephen D.; Székely, Csaba (2015)."Myxozoans exploiting homeotherms".In Okamura, B.; Gruhl, A.; Bartholomew, J.L. (eds.).Myxozoan Evolution, Ecology, and Development.Springer International Publishing. pp. 125–138.doi:10.1007/978-3-319-14753-6_7.ISBN978-3-319-14752-9.S2CID83229156.
- ^Gruhl, Alexander (2015)."Chapter 7 - Myxozoa".In Wanninger, Andreas (ed.).Evolutionary developmental biology of invertebrates.Vol. 1: Introduction, non–bilateria, acoelomorpha, xenoturbellida, chaetognatha. Springer Verlag Wien. pp. 165–177.doi:10.1007/978-3-7091-1862-7_7.ISBN978-3-7091-1861-0.
- ^el Matbouli, M.; Hoffmann, R.W. (1998)."Light and electron microscopic studies on the chronological development ofMyxobolus cerebralisto the actinosporean stage inTubifex tubifex".International Journal for Parasitology.28(1): 195–217.doi:10.1016/s0020-7519(97)00176-8.PMID9504346.
- ^el Matbouli, M.; Hoffmann, R.W.; Mandok, C. (1995)."Light and electron microscopic observations on the route of the triactinomyxon-sporoplasm ofMyxobolus cerebralisfrom epidermis into rainbow trout (Oncorhynchus mykiss) cartilage ".Journal of Fish Biology.46(6): 919–935.doi:10.1111/j.1095-8649.1995.tb01397.x.
- ^abCanning, Elizabeth U.; Okamura, Beth (1 January 2003). "Biodiversity and Evolution of the Myxozoa".Advances in Parasitology.Vol. 56. Academic Press. pp. 43–131.doi:10.1016/S0065-308X(03)56002-X.ISBN978-0-12-031756-1.PMID14710996.
- ^Hartigan, A.; Estensoro, I.; Vancová, M.; Bílý, T.; Patra, S.; Eszterbauer, E.; Holzer, A. S. (16 December 2016)."New cell motility model observed in parasitic cnidarian Sphaerospora molnari (Myxozoa:Myxosporea) blood stages in fish".Scientific Reports.6(1): 39093.Bibcode:2016NatSR...639093H.doi:10.1038/srep39093.PMC5159882.PMID27982057.
- ^Yahalomi, Dayana; Atkinson, Stephen D.; Neuhof, Moran; Chang, E. Sally; Philippe, Hervé; Cartwright, Paulyn; Bartholomew, Jerri L.; Huchon, Dorothée (10 March 2020)."A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome".Proceedings of the National Academy of Sciences.117(10): 5358–5363.Bibcode:2020PNAS..117.5358Y.doi:10.1073/pnas.1909907117.ISSN0027-8424.PMC7071853.PMID32094163.
- ^ Štolc, A. (1899). "Actinomyxidies, nouveau groupe de Mesozoaires parent des Myxosporidies".Bull. Int. l'Acad. Sci. Bohème.12:1–12.
- ^Edwin Lanfranco, 2007,A phylogenetic classification of organisms other than animals.
- ^ Smothers, J.F.; et al. (September 1994). "Molecular evidence that the myxozoan protists are metazoans".Science.265(5179): 1719–1721.Bibcode:1994Sci...265.1719S.doi:10.1126/science.8085160.PMID8085160.
- ^ab A.S. Monteiro; et al. (1 June 2002)."Orphan worm finds a home:Buddenbrockiais a Myxozoan ".Mol. Biol. Evol.19(6): 968–71.doi:10.1093/oxfordjournals.molbev.a004155.PMID12032254.
- ^ J. Zrzavy & V. Hypsa (April 2003). "Myxozoa,Polypodium,and the origin of the Bilateria: The phylogenetic position of "Endocnidozoa" in light of the rediscovery ofBuddenbrockia".Cladistics.19(2): 164–169.Bibcode:2002clad.book.....S.doi:10.1111/j.1096-0031.2003.tb00305.x.S2CID221583517.
- ^ C. L. Anderson, E. U. Canning & B. Okamura (March 1999). "A triploblast origin for Myxozoa?".Nature.392(6674): 346–347.Bibcode:1998Natur.392..346A.doi:10.1038/32801.PMID9537319.S2CID4426181.
- ^ab E. Jímenez-Guri; et al. (July 2007). "Buddenbrockiais a cnidarian worm ".Science.317(116): 116–118.Bibcode:2007Sci...317..116J.doi:10.1126/science.1142024.PMID17615357.S2CID5170702.
- ^Kent M. L.; Margolis L.; Corliss J.O. (1994). "The demise of a class of protists: taxonomic and nomenclatural revisions proposed for the protist phylum Myxozoa Grasse, 1970".Canadian Journal of Zoology.72(5): 932–937.Bibcode:1994CaJZ...72..932K.doi:10.1139/z94-126.
- ^abcFiala, Ivan; Bartošová-Sojková, Pavla; Whipps, Christopher M. (2015)."Classification and Phylogenetics of Myxozoa".In Okamura, Beth; Gruhl, Alexander; Bartholomew, Jerri L. (eds.).Myxozoan Evolution, Ecology, and Development.Springer International Publishing. pp. 85–110.doi:10.1007/978-3-319-14753-6_5.ISBN978-3-319-14752-9.
External links
edit
- "Myxozoa".Tree of Life.
- "Myxozoan researchers network"(main page).