Cryomonadida is a group of

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many forami ...

, that belong to the

Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major euk ...

Characteristics

Members of the Cryomonadida are

single-celled organism A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms an ...

s that are surrounded by a shell comprising layers of organic material. They possess two unequally long

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

, and a single

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 ...

with a distinct

nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis, which is the synthesis of ribosomes. The nucleolus also participates in the formation of sign ...

. They have a laterally located

cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) 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 vacuole ...

, from which

pseudopodia 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 ...

arise.

Systematics

The

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

Cryomonadida was erected in 1993 for the genus ''Cryothecomonas''. In 2005, Sina Adl ''et al.'' did not include the order in their classification, but placed the genus ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' among the

. It became clear, however, that other genera, and taxa known only from

environmental DNA Environmental DNA or eDNA is DNA that is collected from a variety of environmental samples such as soil, seawater, snow or air, rather than directly sampled from an individual organism. As various organisms interact with the environment, DNA ...

, belonged in this group, and so in 2008 Jan Pawlowski placed the Cryomonadida as part of the core Cercozoa. Within the Cercozoa, the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to Cryomonadida is Ebriacea; ''

Pseudodifflugia ''Pseudodifflugia'' is a genus of Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or ...

'' is also closely related. The following genera are included: * Family Rhogostomidae Dumack et al. 2017 ** '' Sacciforma'' Dumack et al. 2017 ** '' Capsellina'' Penard 1909 ** '' Rhogostoma'' Belar 1921 (previously misidentified as ''

Lecythium ''Lecythium'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below ...

'')Adl, S.M. ''et al.'' (2012). The revised classification of eukaryotes. ''Journal of Eukaryotic Microbiology'' 59 (5): 429–514

* Family Protaspidae Cavalier-Smith 1993 ryothecomonadidae Cavalier-Smith 1993** ''

Cryothecomonas Cryomonadida is a group of heterotrophic Rhizaria, that belong to the Cercozoa. Characteristics Members of the Cryomonadida are single-celled organisms that are surrounded by a shell comprising layers of organic material. They possess two unequa ...

'' Thomsen et al. 1991 ** '' Protaspa'' Cavalier-Smith 2011 'Protaspis''_Skuja_1939_non_Bryant_1933.html" ;"title="Protaspis.html" ;"title="'Protaspis">'Protaspis'' Skuja 1939 non Bryant 1933">Protaspis.html" ;"title="'Protaspis">'Protaspis'' Skuja 1939 non Bryant 1933ref name="Hoppenrath"/> ** ''Sinistermonas'' Lee 2015

References

{{Taxonbar, from=Q1142230 Cercozoa orders Thecofilosea