| Litostomatea | |
|---|---|
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| Lacrymaria olor (Haptorida) | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Clade: | Alveolata |
| Phylum: | Ciliophora |
| Subphylum: | Intramacronucleata |
| Infraphylum: | Rhabdophora |
| Class: | Litostomatea Small &Lynn 1981 |
| Typical orders | |
Subclass Haptoria | |
TheLitostomatea are a class ofciliates.[1] The group consists of three subclasses: Haptoria, Trichostomatia and Rhynchostomatia. Haptoria includes mostly carnivorous forms such asDidinium, a species of which preys primarily on the ciliateParamecium. Trichostomatia (trichostomes) are mostlyendosymbionts in the digestive tracts of vertebrates. These include the speciesBalantidium coli, which is the only ciliate parasitic in humans. The group Rhynchostomatia includes two free-living orders previously included among the Haptoria, but now known to be genetically distinct from them, the Dileptida and the Tracheliida.[2][3]
In litostomes, the body cilia arise from structures in thecell cortex calledmonokinetids, which are made up of a single cilium and its associated structures, such asbasal bodies andmicrotubular fibres. These have an ultrastructural arrangement characteristic to the group.
The cell "mouth" (cytostome) isapical or subapical. In trichostomes it lies in a depression, or vestibule, containing modified somatic cilia. In one order, the Entodiniomorphida, the cilia are arranged into tufts or bands, and may be packed together to form syncilia, resembling themembranelles and cirri ofspirotrichs (with which they were originally classified) and other ciliates. However, no true compound cilia occur.
In haptorians the mouth is typically surrounded by a ring of coronal cilia, arising fromdikinetids derived from the anterior of the body kineties, and a ring of characteristicextrusomes calledtoxicysts. These discharge on contact with prey, penetrating and immobilizing them, and beginning digestion. In some forms the mouth is formed only during feeding, and everts to assist in capture. The cytopharynx takes the form of a straight tube, supported by rods ornematodesmata, which dilates greatly during ingestion. This structure is called arhabdos, and is functionally and structurally distinct from thecyrtos found in several other classes.