Chaos (amoeba)
Encyclopedia
Chaos is a genus of giant amoebae
. The largest and best known species, Chaos carolinensis, can reach lengths of 5mm, although most specimens fall between 1 and 3 mm.
Members of the genus closely resemble Amoeba
, and share the same general morphology, producing numerous cylindrical pseudopod
s, each of which is rounded at the tip. However, while Amoeba have a single nucleus
, Chaos can have as many as a thousand. Because of this attribute, C. carolinensis, was once placed in the genus Pelomyxa
along with the other giant multinucleate amoeba, Pelomyxa palustris. Recently, molecular phylogenetic studies of this species have confirmed the view of some earlier researchers that it is more closely related to Amoeba
than to Pelomyxa
. The species is now placed in the independent genus Chaos, a sister group of Amoeba
.
Chaos species are versatile heterotrophs, able to feed on bacteria, algae, other protists, and even small multicellular invertebrates. Like all Amoebozoa
, they take in food by phagocytosis, encircling food particles with its pseudopodia, then enclosing them within a food ball, or vacuole
, where they are broken down by enzymes. The cell does not have a mouth or cytostome
, nor is there any fixed site on the cell membrane at which phagocytosis normally occurs.
The cell's membrane, or plasmalemma, is loose and extremely plastic, allowing the organism to change shape from one moment to the next. The cytoplasm
within the membrane is conventionally described as having two parts: the internal fluid, or endoplasm
, which contains loose granules and food vacuoles, as well as organelles such as nuclei and mitochondria; and a more viscous ectoplasm
around the perimeter of the cell, which is relatively clear and contains no conspicuous granules. Like other lobose amoebae, Chaos move by extending pseudopod
ia. As a new pseudopod is extended, a variable zone of ectoplasm forms at the leading edge and a fountaining stream of endoplasm circulates within. The effort of describing these motions, and explaining how they result in the cell's forward movement, has generated a large body of scientific literature.
saw and depicted an amoeboid he named "the little Proteus." Three years later, Linnaeus gave Rösel's creature the name Volvox chaos. However, because the name Volvox
had already been applied to a genus of flagellate algae, he later changed it to Chaos chaos. In subsequent decades, as new names and species proliferated, accounts of Chaos
, under a variety of synonyms, became so thoroughly entangled with descriptions of similar organisms, that it is virtually impossible to differentiate one historic amoeboid from another. In 1879, Joseph Leidy suggested collapsing all the "common" large, freshwater amoebae into one species, which he proposed to call Amoeba proteus. A dozen species, including several that had been identified as belonging to Chaos, were to be regarded as synonynms of Amoeba proteus. However, in the description he gives of this organism, it is clearly defined as a uninucleate amoeba, unlike the modern Chaos.
In 1900, the biologist H. V. Wilson, at the University of North Carolina, discovered and isolated a giant amoeba that resembled Amoeba proteus but had cellular nuclei numbering in the hundreds. Since there existed already a genus of giant multinucleate amoebae, Pelomyxa, Wilson placed his organism in that taxon, naming it Pelomyxa carolinensis. This amoeba was easily cultivated and became a widely distributed and studied laboratory organism.
In 1926, Asa A. Schaeffer argued that Pelomyxa carolinensis was, in fact, identical to the amoeba that had been seen by Rösel in 1755, the "little Proteus" which Linnaeus had named Chaos chaos. Therefore, he urged that, in keeping with the principle of priority
governing biological nomenclature, the name of the organism should be Chaos chaos. Several investigators argued vigorously against the validity of that name , but others adopted it. A third faction accepted the validity of the genus Chaos for Wilson's amoeba, but retained the second half of the binomial, referring to the organism as "Chaos carolinensis." By the early 1970s, all three names were in use concurrently, by various investigators. However, studies of the fine structure and physiology of the amoeba made it increasingly clear that there were profound differences between it and the other Pelomyxa (including the complete absence, in true Pelomyxa, of mitochondria). Since then, a nomenclatural consensus has emerged, and today the organism is generally known as Chaos carolinensis, as first proposed by Robert L. King and Theodore L. Jahn in 1948.
flow, in the phylum Sarcodina. Molecular phylogenies based on the examination of ribosomal DNA
, have shown that Sarcodina is a polyphyletic grouping: that some amoeboids shared a more recent common ancestor with members of other phyla than with other Sarcodina. Consequently, the amoeboids of Sarcodina have been distributed among two newly-created supergroups, Rhizaria
and Amoebozoa
. Chaos and its close relative, Amoeba, are now placed in the latter, within the order Tubulinida: naked amoebas (lacking a test
, or shell), either monopodial or possessing somewhat cylindrical pseudopods, with non-adhesive uroid (a region at the posterior of the cell which has a crumpled appearance).
While the monophyly
of Amoebozoa has yet to be established, current information confirms the status of Chaos and Amoeba as closely related taxa within the group. However, the same research raises questions about the monophyly of the genus Chaos, since Chaos nobile may be basal to a group containing Chaos carolinensis and at least two species of Amoeba
, as illustrated below, following Pawlowski and Burki (2009):
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
. The largest and best known species, Chaos carolinensis, can reach lengths of 5mm, although most specimens fall between 1 and 3 mm.
Members of the genus closely resemble Amoeba
Amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...
, and share the same general morphology, producing numerous cylindrical pseudopod
Pseudopod
Pseudopods or pseudopodia are temporary projections of eukaryotic cells. Cells that possess this faculty are generally referred to as amoeboids. Pseudopodia extend and contract by the reversible assembly of actin subunits into microfilaments...
s, each of which is rounded at the tip. However, while Amoeba have a single nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, Chaos can have as many as a thousand. Because of this attribute, C. carolinensis, was once placed in the genus Pelomyxa
Pelomyxa
Pelomyxa are giant amoebae, usually 500-800 μm but occasionally up to 5 mm in length. One notable species is P. palustris; other described species may be synonyms, or have been moved to the unrelated genus Chaos...
along with the other giant multinucleate amoeba, Pelomyxa palustris. Recently, molecular phylogenetic studies of this species have confirmed the view of some earlier researchers that it is more closely related to Amoeba
Amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...
than to Pelomyxa
Pelomyxa
Pelomyxa are giant amoebae, usually 500-800 μm but occasionally up to 5 mm in length. One notable species is P. palustris; other described species may be synonyms, or have been moved to the unrelated genus Chaos...
. The species is now placed in the independent genus Chaos, a sister group of Amoeba
Amoeba
Amoeba is a genus of Protozoa.History=The amoeba was first discovered by August Johann Rösel von Rosenhof in 1757. Early naturalists referred to Amoeba as the Proteus animalcule after the Greek god Proteus, who could change his shape...
.
Chaos species are versatile heterotrophs, able to feed on bacteria, algae, other protists, and even small multicellular invertebrates. Like all Amoebozoa
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
, they take in food by phagocytosis, encircling food particles with its pseudopodia, then enclosing them within a food ball, or vacuole
Vacuole
A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain...
, where they are broken down by enzymes. The cell does not have a mouth or cytostome
Cytostome
A cytostome or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles. Only certain groups of protozoa, such as the ciliates and excavates, have cytostomes. Such...
, nor is there any fixed site on the cell membrane at which phagocytosis normally occurs.
The cell's membrane, or plasmalemma, is loose and extremely plastic, allowing the organism to change shape from one moment to the next. The cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
within the membrane is conventionally described as having two parts: the internal fluid, or endoplasm
Endoplasm
Endoplasm generally refers to the inner part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer layer of the cytoplasm....
, which contains loose granules and food vacuoles, as well as organelles such as nuclei and mitochondria; and a more viscous ectoplasm
Ectoplasm
Ectoplasm may refer to:* Ectoplasm , the outer part of the cytoplasm* Ectoplasm , supposed physical substance that manifests as a result of spiritual energy or psychic phenomenon...
around the perimeter of the cell, which is relatively clear and contains no conspicuous granules. Like other lobose amoebae, Chaos move by extending pseudopod
Pseudopod
Pseudopods or pseudopodia are temporary projections of eukaryotic cells. Cells that possess this faculty are generally referred to as amoeboids. Pseudopodia extend and contract by the reversible assembly of actin subunits into microfilaments...
ia. As a new pseudopod is extended, a variable zone of ectoplasm forms at the leading edge and a fountaining stream of endoplasm circulates within. The effort of describing these motions, and explaining how they result in the cell's forward movement, has generated a large body of scientific literature.
Early history and naming controversy
The genus Chaos has had a long and often confusing history. In 1755, Rösel von RosenhofAugust Johann Rösel von Rosenhof
August Johann Rösel von Rosenhof was a German miniature painter, naturalist and entomologist. With his accurate, heavily detailed images of insects he was recognised as an important figure in modern entomology.-Life:Descendant of a "noble family of Austria", Rösel was born August Johannes Rösel...
saw and depicted an amoeboid he named "the little Proteus." Three years later, Linnaeus gave Rösel's creature the name Volvox chaos. However, because the name Volvox
Volvox
Volvox is a genus of chlorophytes, a type of green algae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox developed its colonial lifestyle .-Description:Volvox is the most developed...
had already been applied to a genus of flagellate algae, he later changed it to Chaos chaos. In subsequent decades, as new names and species proliferated, accounts of Chaos
Chaos
- Mythology, philosophy, and religion :* Chaos , the concept in classical creation myths** a chasm or abyss, especially in biblical usage, see Abyss** prima materia, the primordial state from which the cosmos originated...
, under a variety of synonyms, became so thoroughly entangled with descriptions of similar organisms, that it is virtually impossible to differentiate one historic amoeboid from another. In 1879, Joseph Leidy suggested collapsing all the "common" large, freshwater amoebae into one species, which he proposed to call Amoeba proteus. A dozen species, including several that had been identified as belonging to Chaos, were to be regarded as synonynms of Amoeba proteus. However, in the description he gives of this organism, it is clearly defined as a uninucleate amoeba, unlike the modern Chaos.
In 1900, the biologist H. V. Wilson, at the University of North Carolina, discovered and isolated a giant amoeba that resembled Amoeba proteus but had cellular nuclei numbering in the hundreds. Since there existed already a genus of giant multinucleate amoebae, Pelomyxa, Wilson placed his organism in that taxon, naming it Pelomyxa carolinensis. This amoeba was easily cultivated and became a widely distributed and studied laboratory organism.
In 1926, Asa A. Schaeffer argued that Pelomyxa carolinensis was, in fact, identical to the amoeba that had been seen by Rösel in 1755, the "little Proteus" which Linnaeus had named Chaos chaos. Therefore, he urged that, in keeping with the principle of priority
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
governing biological nomenclature, the name of the organism should be Chaos chaos. Several investigators argued vigorously against the validity of that name , but others adopted it. A third faction accepted the validity of the genus Chaos for Wilson's amoeba, but retained the second half of the binomial, referring to the organism as "Chaos carolinensis." By the early 1970s, all three names were in use concurrently, by various investigators. However, studies of the fine structure and physiology of the amoeba made it increasingly clear that there were profound differences between it and the other Pelomyxa (including the complete absence, in true Pelomyxa, of mitochondria). Since then, a nomenclatural consensus has emerged, and today the organism is generally known as Chaos carolinensis, as first proposed by Robert L. King and Theodore L. Jahn in 1948.
Recent Phylogeny
Until quite recently, the genus Chaos was included, along with all other protists that extend lobose pseudopods or move about by protoplasmicProtoplasm
Protoplasm is the living contents of a cell that is surrounded by a plasma membrane. It is a general term of the Cytoplasm . Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and...
flow, in the phylum Sarcodina. Molecular phylogenies based on the examination of ribosomal DNA
Ribosomal DNA
Ribosomal DNA codes for ribosomal RNA. The ribosome is an intracellular macromolecule that produces proteins or polypeptide chains. The ribosome itself consists of a composite of proteins and RNA. As shown in the figure, rDNA consists of a tandem repeat of a unit segment, an operon, composed of...
, have shown that Sarcodina is a polyphyletic grouping: that some amoeboids shared a more recent common ancestor with members of other phyla than with other Sarcodina. Consequently, the amoeboids of Sarcodina have been distributed among two newly-created supergroups, Rhizaria
Rhizaria
The Rhizaria are a species-rich supergroup of unicellular eukaryotes. This supergroup was proposed by Cavalier-Smith in 2002. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods...
and Amoebozoa
Amoebozoa
The Amoebozoa are a major group of amoeboid protozoa, including the majority that move by means ofinternal cytoplasmic flow. Their pseudopodia are characteristically blunt and finger-like,...
. Chaos and its close relative, Amoeba, are now placed in the latter, within the order Tubulinida: naked amoebas (lacking a test
Test (biology)
A test is a term used to refer to the shell of sea urchins, and also the shell of certain microorganisms, such as testate foraminifera and testate amoebae....
, or shell), either monopodial or possessing somewhat cylindrical pseudopods, with non-adhesive uroid (a region at the posterior of the cell which has a crumpled appearance).
While the monophyly
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
of Amoebozoa has yet to be established, current information confirms the status of Chaos and Amoeba as closely related taxa within the group. However, the same research raises questions about the monophyly of the genus Chaos, since Chaos nobile may be basal to a group containing Chaos carolinensis and at least two species of Amoeba
, as illustrated below, following Pawlowski and Burki (2009):