Naegleria gruberi

Heterolobosea Page & Blanton 1985

Diagnosis: Typically amoebae with eruptive pseudopodia, but with alternate ciliated phase, which is often nonfeeding; many species lack the ciliated phase, while some others lack the amoeboid phase; ciliated cells usually with two or four cilia; if capable of feeding usually use a groove-like cytostome; closed mitosis with internal spindle; mitochondrial cristae flattened, often discoidal; discrete dictyosomes not observed. Apomorphy: eruptive pseudopodia, not homologous to eruptive pseudopodia in Amoebozoa.

Characteristics of heterolobose amoebae are:

  • commonly cylindrical and monopodial, rarely flattened
  • usually markedly eruptive
  • with length to 65 µm (rarely more), but usually smaller
  • a few short, fine subpseudopodia
  • usually uninucleate
  • flagellate stages in many taxa
  • cyst-forming, a few spore-forming;
  • mitochondrial cristae discoid;
  • mitosis intranuclear, in most with binary division of nucleolus.

In general, any eruptive limax amoeba without an alternate flattened form should be considered a probable vahlkampfiid. Vahlkampfiid amoebae usually move more rapidly and are on the average thicker (mean L/B <3) than other small limax amoebae. The amoeboid forms of the different genera are very similar. Those of one or two genera may be more irregular than others; e.g., Naegleria amoebae are sometimes temporarily branched when not very active. The amoebae may trail several uroidal filaments formed by adhesion. Species of several genera have a strong tendency to supernumerary nuclei.
All known freshwater/soil vahlkampfiids are cyst-forming, though the ability to encyst sometimes declines after years in culture, especially in the genus Vahlkampfia. Either a promitotic division pattern or the presence of discoid mitochondrial cristae is evidence that a non-sporulating limax amoeba is a vahlkampfiid.
All species without known flagellate stages are classified in the genus Vahlkampfia. However, some strains of species known to have a flagellate stage have failed to produce flagellates under laboratory conditions, and strains may also suffer reduction or loss of ability to produce flagellates after several months in culture, a loss known especially for Paratetramitus, Tetramastigamoeba, Tetramitus and Willaertia. Flagellates should therefore be sought as soon as possible after isolation.
Flagellates are always formed by transformation of amoebae; cysts always give rise to amoebae, as far as known, though these may then transform into flagellates.
Flagellar numbers can varie. A strain which fails to produce flagellates but conforms fully to the other characters of awell described and distinctive species should be classified, at least provisionally, in that species and genus.
Although differences can, with care and experience, be found amongst amoebae, those differences are seldom distinctive enough for identification. The cyst provides the most useful characters for species identification and in at least two cases is important for generic identification. Attention should be given to any variation in cyst structure within a species. The flagellate is, however, the essential distinction amongst genera having such a stage.
(All after Page, 1988)

Cysts of Naegleria gruberi
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