''Polychaos dubium'' is a freshwater
amoeboid
An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and r ...
and one of the larger species of single-celled
eukaryote
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
. Like other
amoebozoa
Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
ns, ''P. dubium'' moves by means of temporary projections called
pseudopod
A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
s. ''P. dubium'' reportedly has one of the largest
genome size
Genome size is the total amount of DNA contained within one copy of a single complete genome. It is typically measured in terms of mass in picograms (trillionths or 10−12 of a gram, abbreviated pg) or less frequently in daltons, or as the tot ...
of any organism known,
though the authors of a 2004 study suggest treating that measurement with caution.
''Polychaos dubium'' was previously known as ''Amoeba dubia''.
The author who named the species later recognized it as different from species of ''
Amoeba
An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...
'', and so designated it the
type species
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
of the genus ''
Polychaos''.
Unlike species of ''Amoeba'', ''P. dubium'' lacks longitudinal ridges on its pseudopods.
[
]
Physical characteristics
A few characteristics distinguish ''Polychaos dubium'' from other species of ''Polychaos''. The crystals floating in its cytoplasm take the shape of flat
bipyramid
In geometry, a bipyramid, dipyramid, or double pyramid is a polyhedron formed by fusing two Pyramid (geometry), pyramids together base (geometry), base-to-base. The polygonal base of each pyramid must therefore be the same, and unless otherwise ...
s, flat plates, or clustered platelets. The
nucleus is ellipsoid in shape, has granules next to the membrane, and lacks an
endosome
Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of the endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membra ...
. The cell is usually polypodal (has many pseudopodia), and the endoplasm and ectoplasm of the
cytoplasm
The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
are clear.
During rapid locomotion, ''P. dubium'' may become monopodial (present only one pseudopod),
[
]
but there are an average of 12 pseudopodia.
[
]
''Polychaos dubium'' has one of the largest
genome
A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
s known for any organism, consisting of 670 billion
base pair
A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
s or 670
Gbp,
[
]
which is over 200 times larger than the
human genome
The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual Mitochondrial DNA, mitochondria. These ar ...
(3.2 Gbp). The authors of one 2004 study, however, suggest treating that measurement with caution, because it was taken before the advent of modern genomic methods.
Ecology and range
''P. dubium'' inhabits freshwater and is herbivorous,
eating algae.
Specimens have been collected in North America, and northern Europe.
References
Further reading
*
External links
Genome News Network
{{Taxonbar, from=Q2714386
Tubulinea
Amoebozoa species