Gromia

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Gromia
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Gromia (1) and some foraminiferans (2–7)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Phylum: Endomyxa
Class: Gromiidea
Order: Gromiida
Family: Gromiidae
Reuss, 1862
Genus: Gromia
Dujardin, 1835

Gromia is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. Gromia are ameboid, producing filose pseudopodia that extend out from the cell's proteinaceous test through 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.

Contents

Gromia were first discovered in shallow waters, with members of the best-characterized species Gromia oviformus often found inhabiting rock surfaces, sediments, or seaweed holdfasts. However, research from the 1990s and early 2000s identified gromiids inhabiting depths up to 4,392 m, leading to several new deep-sea Gromia species being described and recognized. [1]

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

Deep-sea gromiids have also been shown to be important for carbon cycling [1] and denitrification. [3]

History of study

Gromia were first described in the 1835, with G. oviformis gaining prominence because it was often found in the intertidal zones on the British coast. [4] Initially, Gromia were regarded as members of Foraminifera or Filosea, as noted in a review by Cifelli (1990). [5]

Gromia became better characterized throughout the 1960s, when electron microscopy revealed more details on their morphology, including their honeycomb membranes. [6] [1]

The first molecular studies involving Gromia, which sampled G. 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 placed Gromia within the Gromiidea class, 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 – Gromia was shown to be a sister group to Foraminifera. [7] Moreover, within the genus Gromia, studies of the small subunit ribosomal RNA genes of various deep-sea gromiids has revealed species diversity within Gromia, with molecular data tending to correlate with distinct morphologies of the various species’ tests. [9]

Gromia were 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-sea Gromia protists 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

Gromiids inhabit sediments or surfaces of flora in both shallow waters and the deep sea. The best characterized species of shallow-water Gromia is G. 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. oviformis has 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.

Gromia are 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

Gromia members 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 classifying Gromia species, 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 of Gromia.

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 of Gromia. [1]

Life cycle

Gromia have been observed to undergo both asexual and sexual reproduction. In sexual reproduction observed in G. 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

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 species G. sphaerica to 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

Sources: [4] [15]

Related Research Articles

<span class="mw-page-title-main">Xenophyophorea</span> Clade of single-celled organisms

Xenophyophorea is a clade of foraminiferans. Xenophyophores are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of 500 to 10,600 metres. They are a kind of foraminiferan that extract minerals from their surroundings and use them to form an exoskeleton known as a test.

<span class="mw-page-title-main">Foraminifera</span> Phylum of amoeboid protists

Foraminifera are single-celled organisms, members of a phylum or class of Rhizarian protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell of diverse forms and materials. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller number float in the water column at various depths, which belong to the suborder Globigerinina. Fewer are known from freshwater or brackish conditions, and some very few (nonaquatic) soil species have been identified through molecular analysis of small subunit ribosomal DNA.

<span class="mw-page-title-main">Cercozoa</span> Group of single-celled organisms

Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major eukaryotic group to be recognized mainly through molecular phylogenies. They are the natural predators of many species of bacteria. They are closely related to the phylum Retaria, comprising amoeboids that usually have complex shells, and together form a supergroup called Rhizaria.

<span class="mw-page-title-main">Rhizaria</span> Infrakingdom of protists

The Rhizaria are a diverse and species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has been described. This group was used by Cavalier-Smith in 2002, although the term "Rhizaria" had been long used for clades within the currently recognized taxon. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. In the absence of an apomorphy, the group is ill-defined, and its composition has been very fluid. Some Rhizaria possess mineral exoskeletons, which are in different clades within Rhizaria made out of opal, celestite, or calcite. Certain species can attain sizes of more than a centimeter with some species being able to form cylindrical colonies approximately 1 cm in diameter and greater than 1 m in length. They feed by capturing and engulfing prey with the extensions of their pseudopodia; forms that are symbiotic with unicellular algae contribute significantly to the total primary production of the ocean.

<span class="mw-page-title-main">Phaeodarea</span> Class of protists

Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They are distinguished by the structure of their central capsule and by the presence of a phaeodium, an aggregate of waste particles within the cell.

<span class="mw-page-title-main">Lobosa</span> Phylum of protozoans

Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered Sapocribrum, has slender and threadlike (filose) pseudopodia. In current classification schemes, Lobosa is a subphylum, composed mainly of amoebae that have lobose pseudopods but lack cilia or flagella.

<span class="mw-page-title-main">Allogromiida</span> Order of single-celled organisms

The Allogromiida is an order of single-chambered, mostly organic-walled foraminiferans, including some that produce agglutinated tests (Lagynacea). Genetic studies indicate that some foraminiferans with agglutinated tests, previously included in the Textulariida or as their own order Astrorhizida, may also belong here. Allogromiids produce relatively simple tests, usually with a single chamber, similar to those of other protists such as Gromia. They are found as both marine and freshwater forms, and are the oldest forms known from the fossil record.

The Komokiacea are a small group of amoeboid protozoa, considered to be foraminifera, though there have been suggestions that they are a separate group, closely related to foraminifera. Komokiacea are rather large organisms, often exceeding 300 micrometers in maximum dimensions. Along with Xenophyophores they dominate the macro- and megabenthic fauna in the deep sea and are commonly referred to as "giants protists".

<i>Gromia sphaerica</i> Species of single-celled organism

Gromia sphaerica is a large spherical testate amoeba, a single-celled eukaryotic organism and the largest of its genus, Gromia. The genus itself contains about 13 known species, 3 of which were discovered as late as 2005. It was discovered in 2000, along the Oman margin of the Arabian sea, at depths around 1,163 to 1,194 meters. Specimens range in size from 4.7 to 38 millimeters in diameter. The test is usually spherical in shape and honeycombed with pores. There are filaments on the bottom of the organism, where it is in contact with the seafloor, and it is mostly filled with stercomata.

<span class="mw-page-title-main">Testate amoebae</span>

Testate amoebae are a polyphyletic group of unicellular amoeboid protists, which differ from naked amoebae in the presence of a test that partially encloses the cell, with an aperture from which the pseudopodia emerge, that provides the amoeba with shelter from predators and environmental conditions.

<i>Quinqueloculina</i> Genus of single-celled organisms

Quinqueloculina is a genus of foraminifera in the family Miliolidae.

Paleodictyon nodosum is a living creature thought to produce a certain form of burrow nearly identical to Paleodictyon fossils. The modern burrows were found around mid-ocean ridge systems in the Pacific and Atlantic Oceans. Although scientists have collected many of the burrows of Paleodictyon nodosum, they have never seen a live one. What a live specimen would look like is widely debated, with the debate being split into two main sides.

<i>Reticulomyxa</i> Genus of single-celled organisms

Reticulomyxa is a monospecific genus of freshwater foraminiferans. The type species is the unicellular Reticulomyxa filosa. It is found in freshwater environments as well as moist environments, like decomposing matter and damp soils. The heterotrophic naked foraminiferan can feed on microbes as well has larger organisms and is able to be sustained in culture by supplemented nutrients such as wheat germ and oats. The large, multinucleate foraminferan is characteristic for its lack of test and named for the network of connecting pseudopodia surrounding its central body mass. The organism has unique bidirectional cytoplasmic streaming throughout the anastomosing pseudopodia that is some of the fastest reported organelle transport observed. Reticulomyxa was first described in 1949 and is commonly used as a model organism for the unique transport of organelles throughout the cytoplasm of pseudopodia by cytoskeletal mechanisms. Only asexual reproduction of this genus has been observed in culture, but the genome possesses genes related to meiosis suggesting it is capable of sexually reproductive life stages.

<span class="mw-page-title-main">Amoeba</span> Cellular body type

An amoeba, often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of eukaryotic organisms. Amoeboid cells occur not only among the protozoa, but also in fungi, algae, and animals.

Stercomata are extracellular pellets of waste material produced by some groups of foraminiferans, including xenophyophoreans and komokiaceans, Gromia, and testate amoebae. The pellets are ovoid (egg-shaped), brownish in color, and on average measure from 10-20 µm in length. Stercomata are composed of small mineral grains and undigested waste products held together by strands of glycosaminoglycans.

<span class="mw-page-title-main">Monothalamea</span> Taxonomic group of foraminifera

"Monothalamea" is a grouping of foraminiferans, traditionally consisting of all foraminifera with single-chambered tests. Recent work has shown that the grouping is paraphyletic, and as such does not constitute a natural group; nonetheless, the name "monothalamea" continues to be used by foraminifera workers out of convenience.

<i>Occultammina</i> Genus of single-celled organisms

Occultammina is a genus of xenophyophorean foraminifera known from the Atlantic and Pacific oceans. It is notable for being the first known infaunal xenophyophore as well as for being a possible identity for the enigmatic trace fossil Paleodictyon.

<span class="mw-page-title-main">Foraminifera test</span> Shell of a particular type of protist

Foraminiferal tests are the tests of Foraminifera.

Mayorella marianaensis is a species of amoebozoan protist discovered in 2023 in Mariana Trench sediments. It belongs to the order Dermamoebida, a group of naked amoebae with a thick glycocalyx.

Limnofila is a genus of heterotrophic protists that live in freshwater habitats and feed on bacteria. They are also present in the soil ecosystem, where they play an important role as predators of bacteria. They are classified as a single family Limnofilidae and order Limnofilida.

References

  1. 1 2 3 4 5 6 7 8 Rothe, N.; Gooday, A.J.; Cedhagen, T.; Hughes, J. Alan (2011). "Biodiversity and distribution of the genus Gromia (Protista, Rhizaria) in the deep Weddell Sea (Southern Ocean)" (PDF). Polar Biology. 34 (1): 69–81. doi:10.1007/s00300-010-0859-z. S2CID   22228614.
  2. 1 2 3 4 Matz, 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 . PMID   19026540. S2CID   8819675.
  3. 1 2 Høgslund, 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 . PMC   5397464 . PMID   28473806.
  4. 1 2 Hayward, B.W.; le Coze, F.; Gross, O. (2018). "Gromia dujardin". World Foraminifera Database. Retrieved 26 February 2020.
  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 of Gromia oviformis (Sarcodina)". The Journal of Protozoology. 9 (1): 79–87. doi:10.1111/j.1550-7408.1962.tb02585.x.
  7. 1 2 3 Longet, D.; Burki, F.; Flakowski, J.; Berney, C.; Polet, S.; Fahrni, J.; Pawlowski, J. (2004). "Multigene evidence for close evolutionary relations between Gromia and foraminifera". 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. PMID   14658494.
  9. 1 2 Aranda da Silva, A.; Pawlowski, J.; Gooday, A.J. (2006). "High diversity of deep-sea Gromia from the Arabian Sea revealed by small subunit rDNA sequence analysis". Marine Biology. 148 (4): 769–777. doi:10.1007/s00227-005-0071-9. S2CID   85334023.
  10. ↑ Gooday, A.J.; Bowser, S.S.; Bett, B.J.; Smith, C.R. (2000). "A large testate protist, Gromia sphaerica sp. 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. 1 2 3 Aranda 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. 1 2 da 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 of Gromia oviformis [Dujardin]". The Journal of Protozoology. 13 (1): 23–27. doi:10.1111/j.1550-7408.1966.tb01863.x. PMID   5912388.
  15. ↑ "Gromia". World Register of Marine Species (WoRMS). 2012. Retrieved 30 March 2020.
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