Testate amoebae (formerly thecamoebians , Testacea or Thecamoeba) 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.
23-424: Difflugia is the largest genus of Arcellinida , one of several groups of Tubulinea within the eukaryote supergroup Amoebozoa . Arcellinida species produce shells or tests from mineral particles or biogenic elements (e.g. diatom frustules ) and are thus commonly referred to as testate amoebae or shelled amoebae. Difflugia are particularly common in marshes and other freshwater habitats. The genus Difflugia
46-460: A benthic phase during the winter in which they stay immobile near the bottom of the body of water. One way environment can influence characteristics of Difflugia is that there are several freshwater species, which have green endosymbionts or zoochlorellae. The species Difflugia that contain endosymbionts are not considered to be heterotrophs, but instead mixotrophs because they combine being autotrophic and heterotrophic. The source of food depends on
69-452: A combination of both. Past environmental changes can be determined by analysing the composition of fossil tests, including the reconstruction of past climate change . Testate amoebae species have been used to reconstruct hydrological changes over the late Holocene , as a result of individual species possessing a narrow tolerance for ecohydrological conditions such as water-table depth or pH. Fossils of arcellinid testate amoebae date back to
92-435: A new genus Cylindrifflugia . Difflugia are testate amoebae with an agglutinate shell. The test can be composed of various different mineral particles depending on the varying environment. These mineral particles are collectively called xenosomes. All species of the genus Difflugia acquire their xenosomes, from the environment in which they inhabit. Difflugia often have species specific tests, which are arranged based on
115-471: A part of the fragile category are most likely to be constructed from diatom crystals. The environment conditions in which Difflugia lives is important to consider as it greatly influences shell morphology of the species. Shell composition depends on environmental pH and what materials are available. Difflugia can be found living in a large variety of habitats such as freshwater sediments, dry mosses and soil, or lakes. Some species are planktonic and switch to
138-401: A simple test (shell). Arcellinid testate amoebae are commonly found in soils, leaf litter , peat bogs and near/in fresh water. They use their pseudopodia , a temporary cell extension, for moving and taking in food. Like most amoebae, they are generally believed to reproduce asexually via binary fission. However a recent review suggests that sexual recombination may be the rule rather than
161-458: A survey conducted of the African species of Difflugia The 10 shell shape classifications are lobed, collared, compressed, urceolate, globose, ovoid-globose, elongate, acute angled, horned and pyriform. There have been issues coming to a specific consensus about the taxonomy of the genus Difflugia . In 1988, an attempt to characterize and create a phylogenetic tree based upon the composition of
184-418: Is actually composed of several, unrelated groups of organisms. However, some features they all share that have been used to group them together include the presence of a test (regardless of its composition) and pseudopodia that do not anastomose . Testate amoebae can be found in most freshwater environments, including lakes, rivers, cenotes , as well as mires and soils. The strong and resistant nature of
207-550: Is likely that the group has evolved minimally over the course of the Phanerozoic . Phryganellina Organoconcha Volnustoma Hyalospheniformes Excentrostoma Sphaerothecina Longithecina Phryganellina Organoconcha Volnustoma Hyalospheniformes Excentrosoma Cylindrothecina Longithecina Sphaerothecina The classification of Arcellinida, as of 2019: Arcellinida incertae sedis : Testate amoebae The test of some species
230-483: Is produced entirely by the amoeba and may be organic, siliceous or calcareous depending on the species ( autogenic tests ), whereas in other cases the test is made up of particles of sediment collected by the amoeba which are then agglutinated together by secretions from within the cell ( xenogenic tests ). A few taxa ( Hyalospheniidae ) can build either type, depending on the circumstances and availability of foreign material. The assemblage referred to as "testate amoebae"
253-684: The Tonian stage of the Proterozoic , around 789-759 million years ago. The fossils indicate that by 730 million years ago, arcellinids had already diversified into major lineages. Testate amoebae are theorized to be mostly polyphyletic (coming from more than one ancestral type), but testaceafilosea, one group of testate amoebae, are theorized to be monophyletic . Ancient tests of terrestrial fauna are commonly found in fossilized amber, although mid-Cretaceous testate amoeba (i.e., Diffligia , Cucurbitella ) have been found in ancient lake sediments. It
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#1732797876203276-513: The lobose Tubulinea , which include Arcellinida , Difflugina and Phryganellina (within the Amoebozoa ), and the filose Euglyphida (within the SAR supergroup ), although there are smaller groups that also include other testate amoebae. The following table includes a few examples of testate amoebae genera, and reflects their position within
299-424: The classification by Adl et al. (2012), where five supergroups ( Amoebozoa , Opisthokonta , Excavata , SAR and Archaeplastida ) were proposed to classify all eukaryotes . This classification purposefully avoids the use of Linnaean higher category names (phylum, class, order, family). While it has been noted that the names that Adl et al. provide for the clades may result confusing or uninformative regarding
322-473: The environment but across the genus it is found to be mainly algae and fungi. Smaller species of Difflugia are found to consume bacteria as well as algae and fungi. The presence of a test in Difflugia allowed them to be extremely well-preserved in fossils. Difflugia are part of one of the oldest lineages of eukaryotes based on fossil records which date back 750Mya. The only structure of the organisms that
345-500: The exception in amoeboid protists in general, including the Arcellinid testate amoebae. Arcellinida always have a shell or testa. The tests lie outside the cell membrane and consist of organic or mineral materials that are either secreted or incorporate external particles. The testa has a single main opening. Simple tests are made by secretion (autogenous tests), agglutination of foreign material (xenogenous tests), or sometimes
368-407: The particles collected that have been used to produce the test are directly passed on to the daughter cell. Strength of the test is quite variable between the Difflugia species and the strength of the test can be separated into three categories; robust, intermediate and fragile. Robust tests are found to result in a shell with an irregular shape in comparison to the rest of the genus. Shells which are
391-599: The relative degree of phenotypic distinctiveness amongst groups when used in isolation, this system avoids creating superfluous ranks where unnecessary and provides stable group names that can be retained even when a group is moved to a different lineage , as is often the case with protists, as their classification remains in constant review. Plagiopyxis - Quadrulella - Trigonopyxis Traditionally, those species that form large networks of anastomosing pseudopodia , despite some of them having tests, are not counted amongst testate amoebae; this comprises genus Gromia and
414-400: The shell. However, with additional evidence it was found that this is not actually a useful characteristic to evaluate by. In addition, most initial descriptions of Difflugia speciation were completed using light microscopy and therefore lacked the technology to show the details of test structure and composition. The invention of scanning electron microscopy allows for more detail and improved
437-424: The specific shape and size. Most species of Difflugia only contain one nucleus but there are a select few that are multinucleated. In the larger species the nucleus can be vesicular as opposed to the regularly ovular nucleus. All species also contain an epipodium which is a terminal aperture in the protist's structure. The size of Difflugia is found to range from 15μm all the way up to 500μm. During cell division,
460-472: The taxonomic work surrounding Difflugia . Studies surrounding Difflugia have been centered around species found mostly in Europe and Africa. Molecular phylogenetic analyses have revealed that the genus Difflugia , as traditionally defined, is not a monophyletic group. As a result, several globular and oviform species have been transferred to the genus Netzelia and other species have been aggregated in
483-400: The tests allows them to be preserved long after the amoeba has died. These characteristics, along with the sensitivity that some species display to changes in environmental conditions (such as temperature, pH, and conductivity), has sparked their use as bioindicators and paleoclimate proxies in recent years. Testate amoebae are a polyphyletic assemblage. The main testate amoebae groups are
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#1732797876203506-517: Was able to be preserved in the fossils was the test. Therefore, there have been issues differentiating genera such as Cryptodifflugia from Difflugia based on fossil record alone. Another problem arise from the distortion of test and changes to the xenosomes that makes genera difficult to identify from the testate amoebae fossil specimen alone. Arcellinida Arcellinid testate amoebae or Arcellinida , Arcellacean or lobose testate amoebae are single-celled protists partially enclosed in
529-478: Was initially discovered in 1815 by L, Leclerc, but its infra-generic classification as a group is still unclear. The genus Difflugia is the oldest and most diverse of the testate amoebae. It contains more than 300 species and countless subspecies since even minor differences in morphology result in classification as a new species. In 1958, Gauthier-Lièvre and Thomas divided the genus into 10 groups depending on difference in shell morphology. These 10 groups are based on
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