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Gromia

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Gromia
Gromia(1) and someforaminiferans(2–7)
Scientific classificationEdit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Phylum: Endomyxa
Class: Gromiidea
Order: Gromiida
Family: Gromiidae
Reuss, 1862
Genus: Gromia
Dujardin,1835

Gromiais a genus of protists, closely related toforaminifera,which inhabit marine and freshwater environments. It is theonly genusof thefamilyGromiidae.Gromiaareameboid,producing filosepseudopodiathat extend out from the cell's proteinaceoustestthrough a gap enclosed by the cell's oral capsule. The test, a shell made up of protein that encloses the cytoplasm, is made up of several layers of membrane, which resemble honeycombs in shape – a defining character of this genus.

Gromiawere first discovered in shallow waters, with members of the best-characterized speciesGromia oviformusoften found inhabiting rock surfaces, sediments, orseaweedholdfasts.However, research from the 1990s and early 2000s identified gromiids inhabiting depths up to 4,392 m, leading to several new deep-seaGromiaspecies being described and recognized.[1]

A recent study of the deep-sea speciesGromia sphaericarevealed that it produces traces on the seafloor which resemble fossil traces formerly attributed to earlyBilateria(animals with bilateral symmetry); this now calls into question whether such fossil traces are reliable as documentation of early multicellular animal diversification in thePrecambrianera.[2]

Deep-sea gromiids have also been shown to be important forcarbon cycling[1]anddenitrification.[3]

History of study

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Gromiawere first described in the 1835, withG. oviformisgaining prominence because it was often found in the intertidal zones on the British coast.[4]Initially,Gromiawere regarded as members ofForaminiferaor Filosea, as noted in a review by Cifelli (1990).[5]

Gromiabecame better characterized throughout the 1960s, when electron microscopy revealed more details on their morphology, including their honeycombmembranes.[6][1]

The first molecular studies involvingGromia,which sampledG. oviformis,used small subunit (SSU) ribosomal RNA genes and concluded that Gromia were members of Cercozoa, a large group of amoebae with tests and filose pseudopodia.[7]Follow-up studies on this group placedGromiawithin theGromiideaclass, again based on SSU rRNA genes[8] Eventually, when molecular studies combined data from several genes – actin, polyubiquitin, RNA polymerase II and small subunit rRNA genes –Gromiawas shown to be a sister group toForaminifera.[7]Moreover, within the genusGromia,studies of the small subunit ribosomal RNA genes of various deep-sea gromiids has revealed species diversity withinGromia,with molecular data tending to correlate with distinct morphologies of the various species’ tests.[9]

Gromiawere long thought to only inhabit shallow waters, until samples from the Arabian Sea from depths below 1,000 m revealed the first deep-sea gromiid –Gromia sphaerica.[10]Additional species of deep-seaGromiaprotists were later described in waters from the Arabian sea, the European Arctic sea, and off the coast of Antarctica, among other locations, and characterized both morphologically and through molecular studies of their small subunit rRNA genes.[1]

Habitat and ecology

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Gromiids inhabit sediments or surfaces of flora in both shallow waters and the deep sea. The best characterized species of shallow-waterGromiaisG. oviformis.It inhabits intertidal zones and other regions of shallow waters; it is often found attached to rocks, kelp, weeds, Cladophora algae, or within sediments.[9]G. oviformishas been shown to tolerate a temperature range of 0–30 °C.

Deep-sea gromiids have been found in the Arabian sea,[11]off the coast of Antarctica and in the water of the Northwest Atlantic Ocean. They were often collected from the 1,000–3,100 m range.[1]Oxygen levels in gromiid habitats tend to exceed 0.2 mL/L and are therefore not limiting to the organisms’ growth. The temperature tolerance of deep-sea Gromia is uncertain.

Gromiaare thought to acquire nutrients from the organic matter in sediments on the sea floor, as they are often found in areas with abundant phytodetritus.[1]Their apertures face down on sediment surfaces and they use their pseudopodia to feed.[12]

Gromiids found in the deep sea near Oman and Pakistan are often found with Foraminifera, filamentous prokaryotes and bacteria living on their cell surface.[11]Gromiids provide substrates and serve as a surface for attachment to their epibionts.

Description

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Gromiamembers are quite large, ranging from 0.4 mm to 30 mm.[2][1]Their proteinaceous tests vary in shapes, from spherical (e.g.G. oviformis), “sausage shaped”, “grape-shaped”, or pear-shaped (e.g.G. pyriforminis).[11]Test shape is often used for classifyingGromiaspecies, and their morphology tends to align with the molecular data used to differentiate species. The interior of the test is layered with membranes with a honeycomb pattern. These honeycomb membranes are a unique feature ofGromia.

An oral complex containing an aperture (an opening in the test) allows the filose pseudopodia to extend out.[13]The pseudopodia are non-granular, and can form connections to make net-like structures.[7]Gromia use their pseudopodia to crawl along the surface of sediments.[2]Waste pellets ( “stercomata” ) and mineral grains accumulate inside the cell – another characteristic feature ofGromia.[1]

Life cycle

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Gromiahave been observed to undergo both asexual and sexual reproduction. In sexual reproduction observed inG. oviformis,the shells of adult organisms fuse.[14]Gametogenesis and fertilization follow, after which the zygotes mature into amoebulae and exit the parental shells.

Practical importance

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Gromiids are hypothesized to be important for carbon cycling, as they are often found in carbon-rich sediments and feed on detritus.[12]In addition, gromiids have been shown to store high levels of intracellular nitrate, suggesting a role for gromiids in denitrification.[3]

Gromiids have also enriched our understanding of evolutionary history. The ability of the giant, deep-sea speciesG. sphaericato produce tracks on the sea floor has been used to propose a re-evaluation of the use of fossils with similar traces as evidence for dating the origins of animals with bilateral symmetry.[2]

List of species

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Sources:[4][15]

References

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  1. ^abcdefghRothe, N.; Gooday, A.J.; Cedhagen, T.; Hughes, J. Alan (2011)."Biodiversity and distribution of the genusGromia(Protista, Rhizaria) in the deep Weddell Sea (Southern Ocean) "(PDF).Polar Biology.34(1): 69–81.doi:10.1007/s00300-010-0859-z.S2CID22228614.
  2. ^abcdMatz, M.V.; Frank, T.M.; Marshall, N.J.; Widder, E.A.; Johnsen, S. (2008)."Giant deep-sea protist produces bilaterian-like traces".Current Biology.18(23): 1849–1854.doi:10.1016/j.cub.2008.10.028.PMID19026540.S2CID8819675.
  3. ^abHøgslund, S.; Cedhagen, T.; Bowser, S.S.; Risgaard-Petersen, N. (April 2017)."Sinks and sources of intracellular nitrate in Gromiids".Frontiers in Microbiology.8(April): 617.doi:10.3389/fmicb.2017.00617.PMC5397464.PMID28473806.
  4. ^abHayward, B.W.; le Coze, F.; Gross, O. (2018)."Gromia dujardin".World Foraminifera Database.Retrieved26 February2020.
  5. ^Cifelli, R. (1990). "A history of the classification of foraminifera (1826-1933), part 1 Foraminiferal classification from d'Orbigny to Galloway".Cushman Foundation for Foraminiferal Research.1(27): 106.
  6. ^Hedley, R.H.; Bertaud, W.S. (1962). "Electron-microscopic observations ofGromia oviformis(Sarcodina) ".The Journal of Protozoology.9(1): 79–87.doi:10.1111/j.1550-7408.1962.tb02585.x.
  7. ^abcLonget, D.; Burki, F.; Flakowski, J.; Berney, C.; Polet, S.; Fahrni, J.; Pawlowski, J. (2004). "Multigene evidence for close evolutionary relations betweenGromiaandforaminifera".Acta Protozoologica.43(4): 303–311.
  8. ^Cavalier-Smith, T.; Chao, E.E.-Y. (2003). "Phylogeny and classification of phylum Cercozoa (Protozoa)".Protist.154(3–4): 341–358.doi:10.1078/143446103322454112.PMID14658494.
  9. ^abAranda da Silva, A.; Pawlowski, J.; Gooday, A.J. (2006)."High diversity of deep-seaGromiafrom the Arabian Sea revealed by small subunit rDNA sequence analysis ".Marine Biology.148(4): 769–777.doi:10.1007/s00227-005-0071-9.S2CID85334023.
  10. ^Gooday, A.J.; Bowser, S.S.; Bett, B.J.; Smith, C.R. (2000). "A large testate protist,Gromia sphaericasp. nov. (order Filosea), from the bathyal Arabian Sea ".Deep-Sea Research Part II: Topical Studies in Oceanography.47(1–2): 55–73.Bibcode:2000DSRII..47...55G.doi:10.1016/S0967-0645(99)00100-9.
  11. ^abcAranda da Silva, A.; Gooday, A.J. (2009). "Large organic-walled Protista (Gromia) in the Arabian Sea: Density, diversity, distribution and ecology ".Deep Sea Research Part II: Topical Studies in Oceanography.56(6–7): 422–433.Bibcode:2009DSRII..56..422A.doi:10.1016/j.dsr2.2008.12.027.
  12. ^abda Silva, A.A. (2005).Benthic protozoan community attributes in relation to environmental gradients in the Arabian Sea.School of Ocean and Earth Sciences (Ph.D. thesis). University of Southampton, Faculty of Engineering Science and Mathematics.
  13. ^Felts, W.J.L.; Harrison, R.J. (1968). "International review of general and experimental zoology".Journal of Anatomy.103(Part 2): 377.
  14. ^Arnold, Z.M. (1966). "Observations on the sexual generation ofGromia oviformis[Dujardin] ".The Journal of Protozoology.13(1): 23–27.doi:10.1111/j.1550-7408.1966.tb01863.x.PMID5912388.
  15. ^"Gromia".World Register of Marine Species (WoRMS).2012.Retrieved30 March2020.
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