Heterolobosea orPercolozoa, commonly known asamoebomastigotes,[2] is aphylum of protists including manyamoeboflagellates.Naegleria fowleri, the causative agent of the often fatal diseaseamoebic meningitis, is the only member of this phylum infectious to humans. Typically, their life cycle alternates between flagellate and amoeboid stages.
Most Percolozoa are found as bacterivores in soil, fresh water and occasionally in the ocean.[3] The only member of this group that is infectious to humans isNaegleria fowleri, the causative agent of the often fatal diseaseamoebic meningitis.[4] The group is closely related to theEuglenozoa, and share with them the unusual characteristic of havingmitochondria with discoidcristae.[5] The presence of a ventral feeding groove in the flagellate stage, as well as other features, suggests that they are part of theExcavata group.[6]
The amoeboid stage is roughly cylindrical, typically around20–40 μm in length. They are traditionally considered lobose amoebae, but are not related to the others, and unlike them, do not form true lobosepseudopods. 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.[4]
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 generaPercolomonas,Lyromonas, andPsalteriomonas are known only as flagellates, whileVahlkampfia,Pseudovahlkampfia, and mostacrasids 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 thedictyostelids, but the amoebae only aggregate as individuals or in small groups and do not die to form the stalk.[4]
The first broadly sampled comprehensive phylogenomic (phylotranscriptomic) analysis of the group (from 2025) confirmed themonophyly of Heterolobosea and provided a robustly supported backbone of the phylogeny resulting in the revision of the classification of Heterolobosea to the family level.[1]
These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to formsporangia. The entire group is usually called theHeterolobosea, but this may be restricted to members with amoeboid stages.
The Heterolobosea were first defined byPage andBlanton in 1985[11] 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 flagellateStephanopogon.[12]
Cavalier-Smith maintained the Heterolobosea as a class for amoeboid forms. He has defined Percolozoa as "Heterolobosea plusPercolatea classis nov."[5]
^abcPánek, Tomáš; Simpson, Alastair G. B.; Brown, Matthew W.; Dexter Dyer, Betsey (2016), Archibald, John M.; Simpson, Alastair G.B.; Slamovits, Claudio H.; Margulis, Lynn (eds.),"Heterolobosea",Handbook of the Protists, Cham: Springer International Publishing, pp. 1–42,doi:10.1007/978-3-319-32669-6_10-1,ISBN978-3-319-32669-6, retrieved2024-12-14
^Park JS, Simpson AG, Lee WJ, Cho BC (July 2007). "Ultrastructure and phylogenetic placement within Heterolobosea of the previously unclassified, extremely halophilic heterotrophic flagellatePleurostomum flabellatum (Ruinen 1938)".Protist.158 (3):397–413.doi:10.1016/j.protis.2007.03.004.PMID17576098.
^Page, F.C.; R.L. Blanton (1985). "The Heterolobosea (Sarcodina: Rhizopoda), a new class uniting the Schizopyrenida and Acrasidae (Acrasida)".Protistologica.21:121–132.
^Cavalier-Smith, T. (1991). "Cell diversification in heterotrophic flagellates". In D.J. Patterson & J. Larsen (ed.).The Biology of Free-living Heterotrophic Flagellates. Oxford University Press. pp. 113–131.ISBN978-0-19-857747-8.
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