Parabasalid | |
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Two trophozoitesofTrichomonas vaginalis stained with Giemsa | |
Scientific classification | |
Domain: | Eukaryota |
Phylum: | Metamonada |
Subphylum: | Trichozoa |
(unranked): | Parabasalia Honigberg 1973 |
Orders[1] | |
The parabasalids are a group of flagellated protists within the supergroup Excavata. Most of these eukaryotic organisms form a symbiotic relationship in animals. These include a variety of forms found in the intestines of termites[2] and cockroaches, many of which have symbiotic bacteria that help them digest celluloseinwoody plants. Other species within this supergroup are known parasites, and include human pathogens.[3]
The flagella are arranged in one or more clusters near the anterior of the cell. Their basal bodies are linked to parabasal fibers that attach to prominent Golgi complexes, distinctive to the group. Usually they also give rise to a sheet of cross-like microtubules that runs down the center of the cell and in some cases projects past the end. This is called the axostyle, but is different in structure from the axostyles of oxymonads.
Parabasalids are anaerobic, and lack mitochondria, but this is now known to be a result of secondary loss, and they contain small hydrogenosomes which apparently developed from reduced mitochondria.[4] Similar relics have been found in other amitochondriate flagellates, and the parabasalids are probably related to them, forming a group called the metamonads. They lack the feeding grooves found in most others, but this is probably a secondary loss as well.
Before reclassification, the parabasalids were divided into about 7[5] to 10 orders depending on sources. Present classification divides Parabasalia into 4 orders, that is, Trichonymphida, Spirotrichonymphida, Cristamonadida, and Trichomonadida. [1]
The parabsalid Trichomonas vaginalis is not known to undergo meiosis. However, Malik et al.[7] examined T. vaginalis for the presence of 29 genes that function in meiosis and found 27 such genes, including eight genes specific to meiosis in model organisms. These findings suggested that the capability for meiosis, and hence sexual reproduction, was likely present in a recent parabasalid ancestor of T. vaginalis.[7]
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Parabasalia |
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