Tetrahelia

Tetrahelia
Scientific classification
Domain:	Eukaryota
Clade:	Diaphoretickes
Phylum:	Cryptista
Class:	Endohelea
Order:	Axomonadida; Cavalier-Smith in Yabuki et al. 2012 emend. 2022
Family:	Tetraheliidae; Cavalier-Smith 2022
Genus:	Tetrahelia; Cavalier-Smith 2022
Species:	T. pterbica
Binomial name
	Tetrahelia pterbica; (Mikrjukov & Patterson 2000) Cavalier-Smith 2022[1]
Synonyms
	Tetradimorpha pterbica Mikrjukov & Patterson 2000

Tetrahelia (from Latin tetra- 'four', and helio- 'sun') is a genus of four-ciliated protists belonging to the Endohelea, a group of heterotrophic eukaryotes previously considered heliozoa.[2] It is the only genus in the family Tetraheliidae and order Axomonadida. It is a monotypic genus, containing the sole species Tetrahelia pterbica, previously classified as Tetradimorpha. [1]

Description

Tetrahelia are unicellular ciliates with four standard-length centrioles that are shorter than in Heliomorpha and Tetradimorpha, and axopodia generated by a globular centrosome with a distinct granular shell and a microfibrillar 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 dictyosomes on either side of the cell nucleus. The axopodia have several irregularly arranged microtubules and irregularly flattened extrusomes, instead of the kinetocysts seen in Heliomorpha 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.[1]

The life cycle of Tetrahelia contains a lazily swimming, purely flagellate stage with fully retracted axopodia.[1]

References

Cavalier-Smith T (2022). "Ciliary transition zone evolution and the root of the eukaryote tree: implications for opisthokont origin and classification of kingdoms Protozoa, Plantae, and Fungi". Protoplasma. 259: 487–593. doi:10.1007/s00709-021-01665-7. PMC 9010356. PMID 34940909.
Yabuki A, Chao EE, Ishida KI, Cavalier-Smith T (2012). "Microheliella maris (Microhelida ord. n.), an Ultrastructurally Highly Distinctive New Axopodial Protist Species and Genus, and the Unity of Phylum Heliozoa". Protist. 163 (3): 356–388. doi:10.1016/j.protis.2011.10.001. ISSN 1434-4610. PMID 22153838.

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[CavSmith2022-1] Cavalier-Smith T (2022). "Ciliary transition zone evolution and the root of the eukaryote tree: implications for opisthokont origin and classification of kingdoms Protozoa, Plantae, and Fungi". Protoplasma. 259: 487–593. doi:10.1007/s00709-021-01665-7. PMC 9010356. PMID 34940909.

[Microheliella-2] Yabuki A, Chao EE, Ishida KI, Cavalier-Smith T (2012). "Microheliella maris (Microhelida ord. n.), an Ultrastructurally Highly Distinctive New Axopodial Protist Species and Genus, and the Unity of Phylum Heliozoa". Protist. 163 (3): 356–388. doi:10.1016/j.protis.2011.10.001. ISSN 1434-4610. PMID 22153838.