''Tetrahelia'' () is a genus of four-

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

ted

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s belonging to the

Endohelea Endohelea is a proposed clade of eukaryotes that are related to Archaeplastida and the SAR supergroup. They used to be considered heliozoans, but phylogenetically they belong to a group of microorganisms known as Cryptista. Classification Based o ...

, 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 ...

eukaryotes The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of ...

previously considered

heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...

. It is the only genus in the family Tetraheliidae and order Axomonadida. It is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus, containing the sole species ''Tetrahelia pterbica'', previously classified as '' Tetradimorpha''.

Description

''Tetrahelia'' are unicellular

tes with four standard-length

centriole In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers ( Pinophyta), flowering plants ( angiosperms) and most fungi, an ...

s that are shorter than in ''

Heliomorpha ''Heliomorpha'' is a genus of Cercozoa, placed in its own family, Heliomorphidae. It used to be known as "''Dimorpha''", but that name was a junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternat ...

'' and '' Tetradimorpha'', and

axopodia 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 ...

generated by a globular

centrosome In cell biology, the centrosome (Latin centrum 'center' + Greek sōma 'body') (archaically cytocentre) is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell, as well as a regulator of cell-cycle progre ...

with a distinct granular shell and a

microfibril A microfibril is a very fine fibril, or fiber-like strand, consisting of glycoproteins and cellulose. It is usually, but not always, used as a general term in describing the structure of protein fiber, e.g. hair and sperm tail. Its most frequently o ...

lar core. The centrioles are arranged in two pairs: each pair has two parallel centrioles, and the pairs are positioned at 30° of rotation between each other. They are linked at the base by an amorphous material that connects them to the centrosome. There are lateral

dictyosome The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles in ...

s on either side of the cell

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 Nucleu ...

. The axopodia have several irregularly arranged

microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

s and irregularly flattened

extrusome Extrusomes are membrane-bound organelles found in eukaryotic cells that are capable of discharging material contained within to the exterior of the cell. Due to the diversity in structure and function, it is unlikely that different types of extruso ...

s, instead of the kinetocysts seen in ''

'' and '' Tetradimorpha radiata''. The cell size is larger than 60 μm, and the centrosome itself measures between 18 and 20 μm. There is a thick pseudopellicle layer beneath the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

. The life cycle of ''Tetrahelia'' contains a lazily swimming, purely

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

stage with fully retracted axopodia.

References

{{Taxonbar, from=Q116776879 Cryptista genera