Dicyemida,also known asRhombozoa,is a phylum of tinyparasitesthat live in therenal appendagesofcephalopods.
| Dicyemida | |
|---|---|
| |
| Photomicrograph ofDicyema japonicum | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Subkingdom: | Eumetazoa |
| Clade: | ParaHoxozoa |
| Clade: | Bilateria |
| Clade: | Nephrozoa |
| (unranked): | Protostomia |
| (unranked): | Spiralia |
| Clade: | Platytrochozoa |
| (unranked): | Mesozoa |
| Phylum: | Dicyemida |
| Class: | Rhombozoa |
Taxonomy
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Classification is controversial.[1]Traditionally, dicyemids have been grouped with theOrthonectidain the phylumMesozoaand, from 2017, molecular evidence[2][3]appears to confirm this.
However, other molecular phylogenies have placed the dicyemids more closely related to theroundworms.[4]Additional molecular evidence suggests that this phylum is derived from theLophotrochozoa.[5][6]
The phylum (orclassif retained within Mesozoa) contains three families,Conocyemidae,DicyemidaeandKantharellidae,[7]which have sometimes been further grouped intoorders.Authors who treat Dicyemida as an order and separate the family Conocyemidae into a different order (Heterocyemida) prefer 'Rhombozoa' as a more inclusive name for the phylum or class.[3][4][8][9]
Anatomy
editAdult dicyemids range in length from 0.5 to 7 millimetres (0.020 to 0.276 in), and they can be easily viewed through a light microscope.[10]They displayeutely,a condition in which each adult individual of a given species has the same number of cells, making cell number a useful identifying character. Dicyemida lack respiratory, circulatory, excretory, digestive, and nervous systems.
The organism's structure is simple: a single axial cell is surrounded by a jacket of twenty to thirtyciliatedcells. The anterior region of the organism is termed acalotteand functions to attach the parasite to folds on the surface of itshost'srenal appendages.[10]When more than one species of dicyemida exist within the same host, they have distinctly shapedcalottes,which range in shape from conical to disk shaped, or cap shaped.
To this day, there has never been a recorded case of two separate species of dicyemida existing in the same host and having exactly the samecalotte.[3]Species that share similar or even identicalcalotteshave been found on occasion, but have never been found within the same host. Because of the constant variation incalottesize between species (even within one given host) there is very rarely observable competition between the multiple Dicyemida species for habitat or other resources.[5]Calotteshape determines where a dicyemid can comfortably live. In general, dicyemida with conical shapedcalottesfit best within the folds of the kidneys, while those with roundedcalottes(disk or cap shaped) are more easily able to attach to the smooth surfaces of the kidneys.[5]This extreme segregation of habitats allows multiple species of dicyemids to comfortably exist within the same host while not still competing for space or resources (by occupying differentecological niches).
Habitat
editWhile most dicyemid species have been found to prefer to live within specific cephalopods, no one species is unique in their preferences.[11]In fact, It is also almost unheard of that a host infected with a dicyemid is only infected with one species. This means that if a select cephalopod is found to be infected with one species Dicyemid, their body will likely be found to contain organisms with a variety ofcalotteshapes, which means they are infected with multiple different species.[12]On the occasion that similar (but not identical)calotteshapes happen to be present within one host’s body, one species usually ends up dominating the other, indicating that it has adapted more readily to the environment within the host.[12]However, this occurrence is very rare and has only been observed a handful of times. In a study done on octopuses, it was found that Dicyemida that had similarly shapedcalottesrarely coexisted in the same individual host, which suggested a strong level ofcompetitionfor habitat.[13]
In Japan, two types of dicyemid parasites,D. misakienseandD. japonicum,have often been discovered living in the same host. In 1938, when the two species were initially discovered, scientists did not classify them as separate species due to their large amount of morphological similarities. In fact, the only difference between the two species that scientists were able to observe was between the shape of theircalottes.The idea thatD. misakienseandD. japonicumare two different species is still very controversial among scientific groups. Some scientists have speculated that when closely related species of dicyemids coexist in the same region, such as in the case ofD. misakienseandD. japonicum,competition for habitat causes them to evolve to develop two distinctcalotteshapes.[12]
Life cycle
editDicyemids exist in bothasexualandsexualforms. The former predominate in juvenile and immature hosts, and the latter in mature hosts. The asexual stage is termed anematogen;it producesvermiformlarvaewithin the axial cell. These mature through direct development to form more nematogens.[10]Nematogens proliferate in young cephalopods, filling the kidneys.
As the infection ages, perhaps as the nematogens reach a certain density, vermiform larvae mature to formrhombogens,the sexual life stage, rather than more nematogens. This sort of density-responsive reproductive cycle is reminiscent of the asexual reproduction of sporocysts or rediae in larvaltrematodeinfections ofsnails.As with the trematode asexual stages, a few nematogens can usually be found in older hosts. Their function may be to increase the population of the parasite to keep up with the growth of the host.
Rhombogens contain hermaphroditicgonadsdeveloped within the axial cell. These gonads, more correctly termedinfusorigens,self-fertilise to produceinfusoriformlarvae. These larvae possess a very distinctive morphology, swimming about with ciliated rings that resemble headlights. It has long been assumed that this sexually produced infusoriform, which is released when the host eliminates urine from the kidneys, is both the dispersal and the infectious stage. The mechanism of infection, however, remains unknown, as are the effects, if any, of dicyemids on their hosts.[10]
Some part of the dicyemid life cycle may be tied totemperatebenthicenvironments, where they occur in greatest abundance[citation needed].While dicyemids have occasionally been found in the tropics, the infection rates are typically quite low,[14][15]and many potential host species are not infected. Dicyemids have never been reported from truly oceanic cephalopods, who instead host a parasiticciliatefauna[citation needed].Most dicyemid species are recovered from only one or two host species. While not strictly host specific, most dicyemids are only found in a few closely related hosts[citation needed].
References
edit- ^Aruga J, Odaka YS, Kamiya A, Furuya H (25 October 2007)."Dicyema Pax6 and Zic: tool-kit genes in a highly simplified bilaterian".BMC Evol. Biol.7(1): 201.Bibcode:2007BMCEE...7..201A.doi:10.1186/1471-2148-7-201.PMC2222250.PMID17961212.
- ^Tsai-Ming Lu; Miyuki Kanda; Noriyuki Satoh; Hidetaka Furuya (May 2017)."The phylogenetic position of dicyemid mesozoans offers insights into spiralian evolution".Zoological Letters.3(1): 6.doi:10.1186/s40851-017-0068-5.PMC5447306.PMID28560048.
- ^abcDrábková, Marie; Kocot, Kevin M.; Halanych, Kenneth M.; Oakley, Todd H.; Moroz, Leonid L.; Cannon, Johanna T.; Kuris, Armand; Garcia-Vedrenne, Ana Elisa; Pankey, M. Sabrina; Ellis, Emily A.; Varney, Rebecca; Štefka, Jan; Zrzavý, Jan (6 July 2022)."Different phylogenomic methods support monophyly of Enigma tic 'Mesozoa' (Dicyemida + Orthonectida, Lophotrochozoa)".Proceedings of the Royal Society B: Biological Sciences.289(1978): 20220683.doi:10.1098/rspb.2022.0683.PMC9257288.PMID35858055.
- ^abPawlowski J, Montoya-Burgos JI, Fahrni JF, Wüest J, Zaninetti L (October 1996)."Origin of the Mesozoa inferred from 18S rRNA gene sequences".Mol. Biol. Evol.13(8): 1128–32.doi:10.1093/oxfordjournals.molbev.a025675.PMID8865666.
- ^abcKobayashi, M; Furuya, H; Wada, H (2009). "Molecular markers comparing the extremely simple body plan of dicyemids to that of lophotrochozoans: insight from the expression patterns of Hox, Otx, and brachyury".Evol Dev.11(5): 582–589.doi:10.1111/j.1525-142x.2009.00364.x.PMID19754714.S2CID6070504.
- ^Suzuki, TG; Ogino, K; Tsuneki, K; Furuya, H (2010)."Phylogenetic analysis of dicyemid mesozoans (phylum Dicyemida) from innexin amino acid sequences: dicyemids are not related to Platyhelminthes".J Parasitol.96(3): 614–625.doi:10.1645/ge-2305.1.PMID20557208.S2CID25877334.
- ^"Kantharellidae".Integrated Taxonomic Information System.Retrieved5 April2010.
- ^"Rhombozoa".Integrated Taxonomic Information System.Retrieved30 January2024.
- ^"Heterocyemida".Integrated Taxonomic Information System.Retrieved30 January2024.
- ^abcdBarnes, Robert D. (1982).Invertebrate Zoology.Philadelphia, PA: Holt-Saunders International. pp. 248–249.ISBN0-03-056747-5.
- ^Furuya, Hidetaka; Tsuneki, Kazuhiko (May 2003)."Biology of Dicyemid Mesozoans".Zoological Science.20(5): 519–532.doi:10.2108/zsj.20.519.ISSN0289-0003.PMID12777824.
- ^abcFuruya, Hidetaka; Hochberg, F. G.; Tsuneki, Kazuhiko (April 2003)."Calotte morphology in the phylum Dicyemida: niche separation and convergence".Journal of Zoology.259(4): 361–373.doi:10.1017/S0952836902003357.ISSN1469-7998.
- ^Suzuki, Takahito G.; Ogino, Kazutoyo; Tsuneki, Kazuhiko; Furuya, Hidetaka (2010)."Phylogenetic Analysis of Dicyemid Mesozoans (phylum Dicyemida) from Innexin Amino Acid Sequences: Dicyemids Are Not Related to Platyhelminthes".The Journal of Parasitology.96(3): 614–625.doi:10.1645/GE-2305.1.ISSN0022-3395.JSTOR40802479.PMID20557208.
- ^Furuya, Hidetaka[in Japanese](2010). "Systematics, morphology, and life cycle of dicyemid mesozoans ( trung sinh động vật ニハイチュウ の phân loại, hệ thống, sinh hoạt sử )".Jpn. J. Vet. Parasitol.9(1): 128–134.
- ^Hochberg, F.G. (1990). "Diseases caused by protistans and mesozoans".
{{cite journal}}:Cite journal requires|journal=(help)inKinne, Otto.Diseases of Marine animals.Vol. 3. Hamburg: Biologische Anstalt Helgoland. pp. 47–202.
Further reading
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Data related toRhombozoaat Wikispecies
- Furuya H, Tsuneki K (May 2003)."Biology of dicyemid mesozoans".Zool. Sci.20(5): 519–32.doi:10.2108/zsj.20.519.PMID12777824.S2CID29839345.
- Furuya, H.; Hochberg, F. G.; Tsuneki, K. (2003). "Reproductive traits in dicyemids".Marine Biology.142(4): 693–706.Bibcode:2003MarBi.142..693F.doi:10.1007/s00227-002-0991-6.S2CID82265820.
- Hochberg, F.G. (1982). "The" kidneys "of cephalopods: a unique habitat for parasites".Malacologia.23:121–134.
- McConnaughey, B.H. (1951). "The life cycle of the dicyemid Mesozoa".University of California Publications in Zoology.55:295–336.
- Pawlowski J, Montoya-Burgos JI, Fahrni JF, Wüest J, Zaninetti L (October 1996)."Origin of the Mesozoa inferred from 18S rRNA gene sequences".Mol. Biol. Evol.13(8): 1128–32.doi:10.1093/oxfordjournals.molbev.a025675.PMID8865666.