Amoebozoa

Time you got around to sponsoring a child

The Amoebozoa are a group of protists, comprising the majority of the lobose amoeboids and slime molds. The most famous member is Amoeba proteus, often studied as a representative unicellular organism, but it is not actually very common in nature. Many other amoebozoans, however, are frequently found in soils, on vegetation, and in nutrient-rich waters such as bogs and marshes. These include both naked amoebae such as Acanthamoeba and various forms that produce simple shells, previously grouped together as the Testacealobosea. Shells may be formed from secreted materials, as in Arcella, or by cementing together sand and other collected detritus, as in Difflugia.

In contrast to these microscopic members, the Mycetozoa or true slime molds form multinucleate plasmodia that are easily visible to the unaided eye. These ultimately develop fruiting bodies that produce spores, superficially similar to the sporangia of fungi. The spores in turn release biflagellate gametes, which fuse to form new plasmodia. Another group of amoebozoans, the dictyostelids, also form fruiting bodies, but from aggregates of separate amoebae which comes together under unfavourable circumstances. Similar life cycles are found in several unrelated groups, such as the acrasids and myxobacteria.

There is some evidence that the amoebozoans are monophyletic, but their classification and relationships remain uncertain. Patterson united them with the testate filose amoeboids as the ramicristates, based on the common presence of mitochondria with branching tubular cristae. However, genetic studies include the amitochondriate pelobionts and entamoebae and remove the testate lobose amoeboids to the Cercozoa. In the phylogeny proposed by Stechmann and Cavalier-Smith, the Amoebozoa lie near or at the base of the eukaryotes, but this position has also been assigned to the excavates.

References

Patterson, D. J. (1999). The diversity of eukaryotes. American Naturalist 154: S96-S124
Stechmann, A & T Cavalier-Smith (2002). Rooting the eukaryote tree by using a derived gene fusion. Science 297: 89ÃÂÃÂ91.
Fahrni et al. (2003). Phylogeny of Lobose Amoebae Based on Actin and Small-Subunit Ribosomal RNA Genes. Molecular Biology and Evolution 20(11): 1881-6