| Hypotrich | |
|---|---|
| Hypotrich ciliate in family Oxytrichidae | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Alveolata |
| Phylum: | Ciliophora |
| Class: | Spirotrichea |
| Subclass: | Hypotrichia Stein 1859 |
| Orders and Families | |
| |
Thehypotrichs are a group ofciliatedprotozoa, common in fresh water, salt water, soil and moss. Hypotrichs possess compound ciliary organelles called "cirri," which are made up of thick tufts ofcilia, sparsely distributed on theventral surface of the cell. The multiple fused cilia which form a cirrus function together as a unit, enabling the organism to crawl along solid substrates such as submerged debris or sediments. Hypotrichs typically possess a large oral aperture, bordered on one side by a wreath or collar ofmembranelles (small membranous structures made up of fused cilia), forming an "adoral zone of membranelles," or AZM.[2][3][4]
In older systems of classification, the term hypotrich comprised all ciliates possessing a relatively flattened body shape, strong cirri restricted to the ventral surface, and a large oral region (peristome) partially surrounded by an "adoral zone of membranelles".[3] From aphylogenetic point of view, this historic grouping--which included both euplotid ciliates (such asEuplotes andAspidisca), andstichotrichian ciliates (such asOxytricha andUrostyla)--isparaphyletic.[5] Any natural group, orclade, that contains bothEuplotes andOxytricha would also have to include many morphologically dissimilarspirotrich ciliates, such as thetintinnids and theoligotrichs.
In the classification system developed by Denis Lynn in collaboration with Eugene B. Small, the subclass Hypotrichia was restricted to euplotids and one small order of marine ciliates called Kiitrichida, while most of the traditional hypotrichs were placed in the subclass Stichotrichia.[6] However, some prominent researchers—notably, the Austrian ciliatologist Helmut Berger—rejected Lynn's nomenclature, and continued to assign non-euplotid "hypotrich" ciliates, such as oxytrichids and urostyloids, to some variant ofFriedrich von Stein's original order Hypotricha.[7]
In their revised classification of the phylum Ciliophora, published in 2016, Gao et al. place the "stichotrichs" of Lynn & Small in the synonymous subclass Hypotrichia, and place all euplotid and discocephalid ciliates in the subclass Euplotia.[1] The same high-level taxa are used, without ranks, by Adl et al. in their "Revised Classification of Eukaryotes" of 2012.[2]
.jpg)
.jpg)
.jpg)
`