''Polychaos dubium'' is a freshwater
amoeboid
An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudopo ...
and one of the larger species of single-celled
eukaryote. Like other
amoebozoans, ''P. dubium'' moves by means of temporary projections called
pseudopod
A pseudopod or pseudopodium (plural: 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 filament ...
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 (10−12) of a gram, abbreviated pg) or less frequently in daltons, or as the total ...
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; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudop ...
'', and so designated it the
type species
In 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 species that contains the biological type specime ...
of the genus ''
Polychaos''.
Unlike species of ''Amoeba'', ''P. dubium'' lacks longitudinal ridges on its pseudopods.
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]
Physical characteristics
A few characteristics distinguish ''Polychaos dubium'' from other species of ''Polychaos''. The crystals floating in its cytoplasm take the shape of flat
bipyramids, flat plates, or clustered platelets. The
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
* Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucl ...
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 endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membrane can ...
. The cell is usually polypodal (has many pseudopodia), and the endoplasm and ectoplasm of the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
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
In the fields of molecular biology and genetics, 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 g ...
s known for any organism, consisting of 670 billion
base pairs or 670
Gbp
Sterling (abbreviation: stg; Other spelling styles, such as STG and Stg, are also seen. ISO code: GBP) is the currency of the United Kingdom and nine of its associated territories. The pound ( sign: £) is the main unit of sterling, and t ...
,
[
]
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 DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the ...
(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