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Percolozoa

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Percolozoa

Percolozoa
Different stages of Naegleria
Scientific classification
Domain: Eukaryota
Kingdom: Excavata
Phylum: Percolozoa
Cavalier-Smith 1991
Classes, Orders and Families

The Percolozoa are a group of colourless protozoa, including many that can transform between amoeboid, flagellate, and encysted stages.

Terminology and classification

These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to form sporangia. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.

One Heterolobosea classification system is as follows:[1]

Pleurostomum flabellatum has recently been added to Heterolobosea.[2]

Characteristics

Most Percolozoa are found as bacterivores in soil, freshwater, and on feces. There are a few marine and parasitic forms, including the species Naegleria fowleri, which can become pathogenic in humans and is mostly fatal. The group is closely related to the Euglenozoa, and share with them the unusual though not unique characteristic of having mitochondria with discoid cristae. The presence of a ventral feeding groove in the flagellate stage, as well as other features, suggests that they are part of the excavate group.

The amoeboid stage is roughly cylindrical, typically around 20-40 μm in length. They are traditionally considered lobose amoebae, but are not related to the others and unlike them do not form true lobose pseudopods. Instead, they advance by eruptive waves, where hemispherical bulges appear from the front margin of the cell, which is clear. The flagellate stage is slightly smaller, with two or four anterior flagella anterior to the feeding groove.

Usually the amoeboid form is taken when food is plentiful, and the flagellate form is used for rapid locomotion. However, not all members are able to assume both forms. The genera Percolomonas, Lyromonas, and Psalteriomonas are known only as flagellates, while Vahlkampfia, Pseudovahlkampfia, and the acrasids do not have flagellate stages. As mentioned above, under unfavourable conditions, the acrasids aggregate to form sporangia. These are superficially similar to the sporangia of the dictyostelids, but the amoebae only aggregate as individuals or in small groups and do not die to form the stalk.

History

The Heterolobosea were first defined by Page and Blanton in 1985[3] as a class of amoebae, and so only included those forms with amoeboid stages. Cavalier-Smith created the phylum Percolozoa for the extended group, together with the enigmatic flagellate Stephanopogon.[4]

Cavalier-Smith maintained the Heterolobosea as a class for amoeboid forms. He has defined Percolozoa as "Heterolobosea plus Percolatea classis nov."[5]

References

  1. ^ "Heterolobosea". Retrieved 2009-03-25. 
  2. ^ Park JS, Simpson AG, Lee WJ, Cho BC (July 2007). "Ultrastructure and phylogenetic placement within Heterolobosea of the previously unclassified, extremely halophilic heterotrophic flagellate Pleurostomum flabellatum (Ruinen 1938)". Protist 158 (3): 397–413.  
  3. ^ Page, F.C.; R.L. Blanton (1985). "The Heterolobosea (Sarcodina: Rhizopoda), a new class uniting the Schizopyrenida and Acrasidae (Acrasida)". Protistologica 21: 121–132. 
  4. ^ Cavalier-Smith, T. (1991). "Cell diversification in heterotrophic flagellates". In D.J. Patterson & J. Larsen. The Biology of Free-living Heterotrophic Flagellates. Oxford University Press. pp. 113–131. 
  5. ^ Cavalier-Smith T (November 2003). "The excavate protozoan phyla Metamonada Grassé emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa". Int. J. Syst. Evol. Microbiol. 53 (Pt 6): 1741–58.  

External links

  • Tree of Life Heterolobosea
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