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Heterotrich

{{Short description|Class of single-celled organisms}}

{{More citations needed|date=October 2016}}

{{Automatic taxobox

| image = Stentor roeseli composite image.jpg

| image_alt = "Stentor roeselii"

| image_caption = Stentor roeselii

| taxon = Heterotrichida

| authority = Stein 1859

| parent_authority = Stein 1859

| display_parents = 3

| synonyms =

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| subdivision_ranks = Families

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}}

The heterotrichs are a class of ciliates. They typically have a prominent adoral zone of membranelles circling the mouth, used in locomotion and feeding, and shorter cilia on the rest of the body. Many species are highly contractile, and are typically compressed or conical in form.{{Cite book|last1=Lobban|first1=Christopher S.|last2=Schefter|first2=María|date=2016-01-01|chapter=An Integrated Model of the Biology of the Marine Symbiosis Maristentor dinoferus|pages=305–326|editor-last=Witzany|editor-first=Guenther|editor-last2=Nowacki|editor-first2=Mariusz|title=Biocommunication of Ciliates|publisher=Springer International Publishing |isbn=9783319322094 |language=en |doi=10.1007/978-3-319-32211-7_17}} These include some of the largest protozoa, such as Stentor and Spirostomum, as well as many brightly pigmented forms, such as certain Blepharisma.

Etymology

The term heterotrich derives from the ancient Greek {{wikt-lang|grc|ἕτερος}} ({{grc-transl|ἕτερος}}), meaning "another, different", and {{wikt-lang|grc|θρίξ}}, {{wikt-lang|grc|τρίχα|τριχός}} ({{grc-transl|θρίξ, τριχός}}), meaning 'hair',{{Cite book|title=Abrégé du dictionnaire grec français|last=Bailly|first=Anatole|date=1981-01-01|publisher=Hachette|isbn=978-2010035289|oclc=461974285|location=Paris}}{{Cite web|url=http://www.tabularium.be/bailly/|title=Greek-french dictionary online|last=Bailly|first=Anatole|website=www.tabularium.be|access-date=2017-01-24}} because of the contrast between the regular somatic ciliation and that of the oral zone.{{cite book|last=Lynn|first=Denis H.|title=The Ciliated Protozoa: Characterization, Classification, and Guide to the Literature. 3rd Edition.|url=https://archive.org/details/ciliatedprotozoa00lynn_842|url-access=limited|year=2008|publisher=Springer|isbn=978-1-4020-8238-2|pages=[https://archive.org/details/ciliatedprotozoa00lynn_842/page/n158 129]}}

Ultrastructure

A number of ultrastructural details characterize the group. The cilia on the body are in dikinetids, in which either the anterior one or both kinetosomes may be ciliated, and which are associated with fibers composed of overlapping postciliary microtubules, called postciliodesmata and found only in this group and the closely related Karyorelictea. A series of oral polykinetids, each containing two or three rows of kinetosomes, support the membranelles. These run from the left to the anterior of the mouth, and often spiral out of the oral cavity. The macronucleus is divided by external microtubules, whereas in the Karyorelictea it forms by differentiation of micronuclei, and in all other ciliates it is divided by internal microtubules.{{Cite journal|last1=Shazib|first1=Shahed Uddin Ahmed|last2=Vd’ačný|first2=Peter|last3=Kim|first3=Ji Hye|last4=Jang|first4=Seok Won|last5=Shin|first5=Mann Kyoon|title=Phylogenetic relationships of the ciliate class Heterotrichea (Protista, Ciliophora, Postciliodesmatophora) inferred from multiple molecular markers and multifaceted analysis strategy|journal=Molecular Phylogenetics and Evolution|volume=78|pages=118–135|doi=10.1016/j.ympev.2014.05.012|pmid=24859684|year=2014}}

Pigmentation

Many species are highly pigmented, e.g. the blue Stentor coeruleus. In Blepharisma, the red pigment is associated with light sensitivity. Species of blue-pigmented Eufolliculina form extensive mats in the deep sea that have been called "blue mats".{{Cite web|url=http://skepticwonder.fieldofscience.com/2010/05/sunday-protist-blue-mats-of-deep-sea.html|title=Sunday Protist -- Blue Mats of the deep sea: Folliculinopsis|website=skepticwonder.fieldofscience.com|access-date=2017-07-25}}

Systematics

File:Abg4102.F1.large.jpg (Blepharismidae)NCBI: [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2528046 Pseudoblepharisma tenue] (species) and its two photosynthetic endosymbionts Chlorella sp. K10 and Ca. Thiodictyon intracellulare (Chromatiaceae)NCBI: [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2784338 Thiodictyon endosymbiont of Pseudoblepharisma tenue] (species){{cite journal |last1=Muñoz-Gómez |first1=SA |last2=Kreutz |first2=M |last3=Hess |first3=S |title=A microbial eukaryote with a unique combination of purple bacteria and green algae as endosymbionts. |journal=Science Advances |date=June 2021 |volume=7 |issue=24 |doi=10.1126/sciadv.abg4102 |pmid=34117067|pmc=8195481 |bibcode=2021SciA....7.4102M }}]]

Early classification schemes by Otto Bütschli, Alfred Kahl, Emmanuel Fauré-Fremiet, and John O. Corliss classified the heterotrichs as a subgroup of spirotrichs. They included groups such as Armophorida, Odontostomatida, Licnophorida, Clevelandellida, and Plagiotomida within the Heterotrichea. However, more recent classification systems, which have incorporated information from molecular phylogenetics, place the above groups within the Intramacronucleata, because they are not closely related to the "core" heterotrichs at all. Almost all of the "true" heterotrichs belong to a single order, Heterotrichida.

In the classification scheme of Lynn (2008), the order Heterotrichida contains the following nine families:

Two new families were established in 2014 on the basis of molecular phylogenies:

References

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Category:Ciliate classes