Amoebaea phylum Amoebozoa Lobosa

The lobose Amoebaea consist of families in the Gymnamoebae, which represent the true naked amoebae (Fig. 1.9). Microtubules do not appear to be involved in pseudopodial stiffening or motility (Hausmann

Amoeba With Cuticle
(B) Hartmanella, (C) Deueteramoeba. Scale bar 10 ^m.

and Hulsmann, 1996). Cilia and centrioles are missing, and micro-tubules are limited to the mitotic spindle. Mitochondria possess branching tubular cristae. The cell membrane is naked, but species tend to have a thick glycoprotein layer (glycocalyx) and some genera have microscales (Dactylamoeba and Platyamoeba), glycostyles (Vanella) or a thickened cuticle (Mayorella), which are seen by transmission electron microscopy only. The free-living soil Gymnamoebae are essentially bac-terivorous, supplemented by pinocytosis. Certain larger species may be cytotrophic on protozoa or other amoebae. Many genera are facultative fungivores (Old and Chakraborty, 1986) but some are obligate fungi-vores, such as Deueteramoeba. Cells can be only 5 ^m in diameter but more usually 8-20 ^m. Exceptionally, some aquatic species of amoeba can be up to several millimetres. Gymnamoebae are usually recognized as belonging to a particular family by their overall shape during locomotion. The principal families encountered in soil samples are presented in Table 1.1, and Lee et al. (2001) provide a useful six step identification key to families by light microscopy. Further identification and species designation require ultrastructure and DNA sequencing, as failing to do so will probaby lead to argument rather than agreement between systematists. However, many genera are tentatively identifiable with light microscopy. There clearly are species that are early colonizers and r-selected (such as Acanthamoeba), whereas other species appear later in the succession of species in decomposing litter (such as Mayorella), and yet other species are encountered only in more stable environments. Some species are particularly adapted to dry conditions, such as the tiny Platyamoeba, when other species are no longer active. Most field sites have a small number of abundant species that vary in their activity period with the seasons and daily abiotic conditions, and a large number of rarer species.

Table 1.1. Selected families of class Amoebaea with edaphic genera.

Families

Selected genera

Acanthamoebidae

Acanthamoeba, Protacanthamoeba

Amoebidae

Deueteramoeba, mostly aquatic genera

Cochliopodiidae

Cochliopodium

Echinamoebidae

Echinamoeba

Gephyramoebida

Gephyramoeba

Hartmannellidae

Glaeseria, Hartmannella, Saccameba

Hyalodiscidae

Flamella, Hyalodiscus

Paramoebidae

Dactylamoeba, Mayorella

Thecamoebidae

Thecamoeba, Thecochaos, Sappinia, Sermamoeba

Vannellidae

Discamoeba, Pessonella, Platyamoeba, Vanella

Leptomyxidae

Leptomyxa, Rhizamoeba (these are eruptive monopodial species)

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