Heterolobosea

Heterolobosea or Percolozoa, commonly known as amoebomastigotes, is a phylum of protists including many amoeboflagellates. Naegleria fowleri, the causative agent of the often fatal disease amoebic meningitis, is the only member of this phylum infectious to humans. Typically, their life cycle alternates between flagellate and amoeboid stages.

Characteristics

Most members of this phylum are bacterivores found in soil, fresh water and occasionally in the ocean. The only member of this phylum that is infectious to humans is Naegleria fowleri, the causative agent of the often fatal disease amoebic meningitis. The group is closely related to the Euglenozoa, and share with them the unusual 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 Excavata group.

The amoeboid stage is roughly cylindrical, typically around 20Ã¢ÂÂ40 ÃÂ¼m 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 most 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.

Phylogeny

The first broadly sampled comprehensive phylogenomic (phylotranscriptomic) analysis of the group (from 2025) confirmed the monophyly of Heterolobosea and provided a robustly supported backbone of the phylogeny resulting in the revision of the classification of Heterolobosea to the family level.

The basal split of the cladogram has been confirmed between the subphyla Pharyngomonada (monotypic, with a sole family Pharyngomonadidae) and Tetramitia. In Tetramitia, two main clades (new classes) were identified: Selenaionea, consisting of two orders Neovahlkampfiida and Selenaionida in previously unsuspected but fully supported sister relationship, and Eutetramitea, consisting of orders Creneida, Lyromonadida, Naegleriida (new, including acrasid slime molds), Percolomonadida and Pseudociliatida (represented by the single genus Stephanopogon; not included in the new analysis but analyses based on 18S rRNA gene sequences have repeatedly shown its close relationship to Percolomonadida with high statistical support):

Taxonomy

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:

Order Schizopyrenida
Family Vahlkampfiidae
Family Gruberellidae
Order Acrasida
Family Acrasidae

Pleurostomum flabellatum has recently been added to Heterolobosea.

Phylum Percolozoa Cavalier-Smith 1991

Subphylum Pharyngomonada Cavalier-Smith 1991
Class Pharyngomonadea Cavalier-Smith 2008 [Macropharyngomonadidea]
Order Pharyngomonadida Cavalier-Smith 2008 [Macropharyngomonadida]
Family Pharyngomonadidae Cavalier-Smith 2008 [Macropharyngomonadidae Cavalier-Smith 2008]
Genus Pharyngomonas Cavalier-Smith 2008 [Macropharyngomonas nomen nudum]
Subphylum Tetramitia Cavalier-Smith 1993 em. Cavalier-Smith 2008
Genus ?Costiopsis Senn 1900
Genus ?Hoehnemastix Skvortzov 1974
Genus ?Planiosculum Szabados 1948
Genus ?Protomyxomyces Cunningham 1881
Genus ?Protonaegleria Michel & Raether 1985
Genus ?Pseudovahlkampfia Sawyer 1980
Genus ?Schizamoeba Davis 1926
Genus ?Tetramastigamoeba Singh & Hanumaiah 1977
Genus ?Trimastigamoeba Whitmore 1911
Genus ?Wasielewskia Hartmann & Schuessler 1913
Family Euhyperamoebidae Goodkov & Seravin 1984 [Hyperamoebidae Goodkov, Seravin & Railkin 1982]
Genus Euhyperamoeba Goodkov & Seravin 1984 [Hyperamoeba Goodkov, Seravin & Railkin 1982 non Alexeieff 1923]
Class Lunosea Cavalier-Smith 2021
Order Selenaionida HanouskovÃÂ¡, TÃÂ¡borskÃÂ½ & ÃÂepiÃÂka 2018
Family Selenaionidae HanouskovÃÂ¡, TÃÂ¡borskÃÂ½ & ÃÂepiÃÂka 2018
Genus Selenaion Park, De Jonckheere & Simpson 2012
Genus Dactylomonas HanouskovÃÂ¡, TÃÂ¡borskÃÂ½ & ÃÂepiÃÂka 2018
Class Neovahlkampfiea Cavalier-Smith 2021
Order Neovahlkampfiida Cavalier-Smith 2021
Family Neovahlkampfiidae HanouskovÃÂ¡, TÃÂ¡borskÃÂ½ & ÃÂepiÃÂka 2018
Genus Neovahlkampfia Brown & de Jonckheere 1999
Class Lyromonadea Cavalier-Smith 1993
Order Lyromonadida Cavalier-Smith 1993
Family Gruberellidae Page & Blanton 1985
Genus Gruberella Page 1984 non Gruber 1889 non Corliss 1960
Genus Oramoeba de Jonckheere et al. 2011
Genus Stachyamoeba Page 1975
Genus Vrihiamoeba Murase, Kawasak & Jonckheere 2010
Family Paravahlkampfiidae
Genus Fumarolamoeba De Jonckheere, Murase & Opperdoes 2011
Genus Parafumarolamoeba Geisen et al. 2015
Genus Paravahlkampfia Brown & de Jonckheere 1999
Family Plaesiobystridae
Genus Euplaesiobystra Park et al. 2009
Genus Heteramoeba Droop 1962
Genus Pernina El Kadiri, Joyon & Pussard 1992
Family Psalteriomonadidae Cavalier-Smith 1993 [Lyromonadidae Cavalier-Smith 1993]
Genus Harpagon PÃÂ¡nek et al. 2012
Genus Monopylocystis O'Kelly et al. 2003
Genus Psalteriomonas Broers et al. 1990 [Lyromonas Cavalier-Smith 1993]
Genus Pseudoharpagon PÃÂ¡nek et al. 2012
Genus Pseudomastigamoeba
Genus Sawyeria O'Kelly et al. 2003
Class Heterolobosea Page & Blanton 1985
Order Acrasida SchrÃÂ¶ter 1886
Family Acrasidae van Tieghem 1880 ex Hartog 1906
Genus Acrasis van Tieghem 1880
Genus Allovahlkampfia Walochnik & Mulec 2009
Genus Pocheina Loeblich & Tappan 1961 [Guttulina Cienkowski 1873 non D'Orbigny 1839]
Genus Solumitrus Wang et al. 2011
Order Naegleriida Starobogatov 1980
Genus Marinamoeba De Jonckheere et al. 2009
Family Tulamoebidae Kirby et al. 2015
Genus Aurem Jhin & Park 2018
Genus Pleurostomum Namyslowski 1913
Genus Tulamoeba Park et al. 2009
Family Naegleriidae Kudo 1954 [Schizopyrenidae Singh 1951 ex Singh 1952; Bistadiidae Doflein 1916]
Genus Naegleria AlÃÂ©xÃÂ©ieff 1912 [Adelphamoeba Napolitano, Wall & Ganz 1970; Didascalus Singh 1952; Schizopyrenus Singh 1951 ex Singh 1952]
Genus Willaertia de Jonckheere et al. 1984
Order Tetramitida Doweld 2001
Family Vahlkampfiidae Jollos 1917 s.s.
Genus Tetramitus Perty 1852 [Copromastix Aragao 1916; Learamoeba Sawyer et al. 1998, Paratetramitus Darbyshire, Page & Goodfellow 1976, Singhamoeba Sawyer, Nerad & Munson 1992]
Genus Vahlkampfia Chatton & LaLung-Bonnaire 1912 [Guttulidium Frenzel 1892]
Order Creneida Cavalier-Smith 2021
Family Creneidae PÃÂ¡nek et al. 2014
Genus Creneis PÃÂ¡nek et al. 2014
Order Percolomonadida Cavalier-Smith 1993
Family Barbeliidae Arndt 2023
Genus Barbelia Arndt 2021
Genus Nonamonas Hohlfeld, Meyer & Arndt 2023
Family Lulidae Hohlfeld & Arndt 2023
Genus Lula Arndt, Nitsche & Carduck 2021
Family Percolomonadidae Cavalier-Smith 1993 [Choanogasteraceae]
Genus Percolomonas Fenchel & Patterson 1986 [Choanogaster Pochmann 1959]
Family Stephanopogonidae Corliss 1961
Genus Nakurumonas Carduck, Nitsche & Arndt 2021
Genus Stephanopogon Entz 1884

History

The Heterolobosea were first defined by Page and Blanton in 1985 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 Stephanopogon.

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

References

External links

Tree of Life Heterolobosea