Rhizopoda

　

WordNet

1. creeping protozoans: amoebas and foraminifers (同)subclass Rhizopoda

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/05/26 23:06:55」(JST)

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Foraminiferan (Ammonia tepida)

Amoeboids are single-celled life-forms characterized by an irregular shape.

"Amoeboid" and "amœba" are often used interchangeably even by biologists, and especially refer to a creature moving by using pseudopodia. Most references to "amoebas" or "amoebae" are to amoeboids in general rather than to the specific genus Amoeba. The genus Amoeba and amoeboids in general both derive their names from the ancient Greek word for change.

shape and ==Structure== Amoeboids move using pseudopodia, which are bulges of cytoplasm.

Amoebas breathe using their entire cell membrane that is constantly immersed in water. Excess water can cross into the cytosol. Amoebas have a contractile vacuole to expel excess water.

Food sources vary in amoeboids. They may consume bacteria or other protists. Some are detritivores and eat dead organic material. They extend a pair of pseudopodia around food. They fuse to make a food vacuole which then fuses with a lysosome to add digestive chemicals. Undigested food is expelled at the cell membrane.

Amoebas use pseudopodia to move and feed. They are powered by flexibe microfilaments near the membrane. Microfilaments are at least 50% of the cytoskeleton. The other parts are more stiff and are composed of intermediate filaments and microtubules. These are not used in amoeboid movement, but are stiff skeletons on which organelles are supported or can move on.

The shells of amoebas are often composed of calcium. The proteins or materials are synthesised in the cell and exported just outside the cell membrane.

Multicellular amoebas: Slime molds

Main article: Slime mold

Amoebas seem to have connections with two phyla (now defunct) composed of multicellular organisms of the lineage of fungus-like protists, the so-called slime molds. These two defunct phyla were the Myxomycota (i.e., plasmodial slime molds, now classified in the taxon Myxogastria), and Acrasiomycota (i.e. cellular slime molds, now divided into the taxa Acrasida and Dictyosteliida). These two phyla use amoeboid movement in their feeding stage. The former is basically a giant multinucleate amoeba, while the latter lives solitary until food runs out; in which a colony of these functions as a unit. Myxomycete slime molds use amoeboid gametes, as well.

Diversity

They have appeared in a number of different groups. Some cells in multicellular animals may be amoeboid, for instance human white blood cells, which consume pathogens. Many protists also exist as individual amoeboid cells, or take such a form at some point in their life-cycle. The most famous such organism is Amoeba proteus; the name amoeba is variously used to describe its close relatives, other organisms similar to it, or the amoeboids in general.

Classification

As amoebas themselves are polyphyletic and subject to some imprecision in definition, the term "amoeboid" does not provide identification of an organism, and is better understood as description of locomotion.

When used in the broader sense, the term can include many different groups. One source includes 97 different genera. Others include far fewer.

Older classification

In older classification systems, amoeboids, under the taxon name Sarcodina, had been divided into several morphological categories based on the form and structure of their pseudopods.

Amoeboids with pseudopods supported by regular arrays of microtubules were called actinopods, whereas those that weren't were called rhizopods, which were further subdivided into lobose, filose, and reticulose amoebae. In contrast to "rhizopods", where most of their morphologies can be mapped to modern classification systems, "actinopods" appear to be extensively polyphyletic. Actinopods are divided into radiolaria and heliozoa (itself a polyphyletic grouping).

Finally, there was also a strange group of giant marine amoeboids, the xenophyophores, that did not fall into any of these categories.

Modern classification

More modern classifications are based upon cladistics. It has been stated that most amoeboid are now grouped in Amoebozoa or Rhizaria. However, in contexts where "amoeboid" is defined more loosely, there are many amoeboid species that are in the Excavata clade.

Phylogenetic analyses place these genera into the following groups (not all of these are considered amoeboid (or "amoebas") by all sources):

Grouping	Genera	Morphology
Amoebozoa	Lobosea: Acanthamoeba, Amoeba, Balamuthia, Chaos, Clydonella, Discamoeba, Echinamoeba, Filamoeba, Flabellula, Gephyramoeba, Glaeseria, Hartmannella, Hydramoeba, Korotnevella (Dactylamoeba), Leptomyxa, Lingulamoeba, Mastigina, Mayorella, Metachaos, Neoparamoeba, Paramoeba, Polychaos, Phreatamoeba, Platyamoeba, Protoacanthamoeba, Rhizamoeba, Saccamoeba, Sappinia, Stereomyxa, Thecamoeba, Trichamoeba, Trichosphaerium, Unda, Vannella, Vexillifera Conosa: Endamoeba, Entamoeba, Hyperamoeba, Mastigamoeba, Mastigella, Pelomyxa	Lobose pseudopods (Lobosea): Lobose pseudopods are blunt, and there may be one or several on a cell, which is usually divided into a layer of clear ectoplasm surrounding more granular endoplasm.
Rhizaria	Cercozoa: Filosa: Monadofilosa: Gyromitus, Paulinella Granofilosea: Endomyxa: Proteomyxidea: Vampyrella Gromiidea Ascetosporea Foraminifera Radiolaria	Filose pseudopods (Filosa): Filose pseudopods are narrow and tapering. The vast majority of filose amoebae, including all those that produce shells, are placed within the Cercozoa together with various flagellates that tend to have amoeboid forms. The naked filose amoebae also includes vampyrellids. Reticulose pseudopods (Endomyxa): Reticulose pseudopods are cytoplasmic strands that branch and merge to form a net. They are found most notably among the Foraminifera, a large group of marine protists that generally produce multi-chambered shells. There are only a few sorts of naked reticulose amoeboids, notably the gymnophryids, and their relationships are not certain. Radiolarians are a subgroup of actinopods that are now grouped with rhizarians.
Excavata	Heterolobosea: Vahlkampfiidae: Monopylocystis, Naegleria, Neovahlkampfia, Paratetramitus, Paravahlkampfia, Psalteriomonas, Sawyeria, Tetramitus, Vahlkampfia, Willaertia Gruberellidae: Gruberella, Stachyamoeba Parabasalidea: Dientamoeba, Histomonas Other: Rosculus, Acrasis, Heteramoeba, Learamoeba, Stygamoeba, Plaesiobystra, Tulamoeba	The Heterolobosea, includes protists that can transform between amoeboid and flagellate forms.
Chromalveolate	Heterokont: Hyalodiscus, Labyrinthula Alveolata: Pfiesteria	Hyalodiscus and Pfiesteria are sometimes considered to have amoeboid characteristics.
Nucleariid	Micronuclearia, Nuclearia	Nucleariids appear to be close relatives of animals and fungi.
Ungrouped/ unknown	Adelphamoeba, Astramoeba, Cashia, Dinamoeba, Flagellipodium, Flamella, Gibbodiscus, Gocevia, Hollandella, Iodamoeba, Malamoeba, Nollandia, Oscillosignum, Paragocevia, Parvamoeba, Pernina, Pontifex, Protonaegleria, Pseudomastigamoeba, Rugipes, Striamoeba, Striolatus, Subulamoeba, Theratromyxa, Trienamoeba, Trimastigamoeba, Vampyrellium

Pathogenic interactions with other organisms

Some amoeboids can infect other organisms pathogenically (causing disease):

• Entamoeba histolytica is the cause of amoebiasis, or amoebic dysentery.
• Naegleria fowleri (the "brain-eating amoeba") is a fresh-water-native species that can be fatal to humans if introduced through the nose.
• Acanthamoeba can cause amoebic keratitis and encephalitis in humans.
• Balamuthia mandrillaris is the cause of (often fatal) granulomatous amoebic meningoencephalitis

References

External links

• The Amoebae website brings together information from published sources.
• Amoebas are more than just blobs
• Sun Animacules and Amoebas
• Molecular Expressions Digital Video Gallery: Pond Life - Amoeba (Protozoa) Some good, informative Amoeba videos.
• Amoebae: Protists Which Move and Feed Using Pseudopodia at the Tree of Life web project

English Journal

• Diversity and dynamics of microbial communities at each step of treatment plant for potable water generation.

• Lin W1, Yu Z2, Zhang H1, Thompson IP3.
• Water research.Water Res.2014 Apr 1;52:218-30. doi: 10.1016/j.watres.2013.10.071. Epub 2013 Nov 7.
• The dynamics of bacterial and eukaryotic community associated with each step of a water purification plant in China was investigated using 454 pyrosequencing and qPCR based approaches. Analysis of pyrosequencing revealed that a high degree diversity of bacterial and eukaryotic communities is present
• PMID 24268295

• The life history of Flabellula baltica Smirnov (Gymnamoebae, Rhizopoda): adaptations to a spatially and temporally heterogeneous environment.

• Fenchel T1.
• Protist.Protist.2010 Apr;161(2):279-87. doi: 10.1016/j.protis.2009.10.005.
• The polymorphic life history of the marine naked amoeba Flabellula baltica was studied. It can be interpreted in terms of adaptations to an environment that is patchy in time and space and it represents trade-off between longevity during starvation and the ability to initiate multiplication soon aft
• PMID 20018561

• A multivariate statistical evaluation of the "acolla-complex" of Corythionella species, including a description of C. darwini n. sp. (Rhizopoda: Filosea or Rhizaria: Cercozoa).

• Nicholls KH1.
• European journal of protistology.Eur J Protistol.2009 Aug;45(3):183-92. doi: 10.1016/j.ejop.2008.11.001. Epub 2009 Feb 10.
• The testate amoebid genus Corythionella inhabits beach sands and includes three marine and two freshwater species of the "acolla-complex", all characterized by a poorly developed flared collar surrounding the pseudostomal aperture. Multivariate statistical methods (cluster analysis, principal coordi
• PMID 19211235

Japanese Journal

• 皇居の内濠より得られた原生動物,輪虫類,鰓脚類および橈脚類.II.

• 田中 正明,武田 正倫,永野 真理子
• 国立科学博物館専報 43, 419-439, 2006
• … 10 species of 8 genera in the Protozoa (8 species of Rhizopoda, and 2 species of Chiliatea), 22 species (including variety and forma) of 12 genera in the Rotatoria, 1 species of the Gastrotricha, 1 species of the Nematoda, 15 species of 13 genera in the Arthropoda (13 species of Crustacea, and 2 species of Insecta). …
• NAID 110005998921

• Accurate enumeration and identification of Testacea (Protozoa, Rhizopoda) in forest soil using scanning electron microscopy

• Aoki Yoshiyuki
• Journal of Microbiological Methods 55, 791-795, 2003
• NAID 120000978666

Related Links

• Sarcodia: Rhizopoda - Protist Information Server

根足虫の解説と画像 ... References Hausmann & Hülsmann, 1996, Protozoology, Thieme Medical Pub. 岩波・生物学辞典・第4版, 1996, 岩波書店. Margulis, L., Corliss, J.O., Melkonian, M. and Chapman, D.J. (eds.) , 1990, Handbook ...

• Rhizopoda - definition of Rhizopoda by Medical dictionary

Rhizopoda /Rhi·zop·o·da/ (ri-zop´ah-dah) a superclass of protozoa of the subphylum Sarcodina, comprising the amebae. Rhizopoda [ri-zop´ah-dah] a superclass of protozoa comprising the amebae, which move about and acquire food ...

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「根足虫類」

「根足虫類」

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Rhizopoda

• 赤痢アメーバ(Entameoba histoytica)