This website includes those groups of protists traditionally lumped under the name "amoebae". Protists are defined only as a confederation of eukaryote organisms lacking the tissue level of organization seen in plants, animals, and fungi. The term "amoebae" is used for those protists that move and feed by means of cytoplasmic streaming. This unique method of locomotion is called amoeboid movement. Amoebae are also characterized by an irregular shape and the lack of a constant body form. The name "amoeba" is derived from an ancient Greek word, that means "changing". Cilia, if present, are usually restricted to developmental stages. A characteristic feature of amoeboid locomotion is the formation of pseudopodia, temporary cytoplasmic extensions.
Amoeboid protists comprise a large and very diverse group with over 15,000 described species. Most are free-living, ubiquitous organisms that are widespread in nature and can be found in nearly any moist or aquatic habitat, aerobic or anaerobic. Some amoeboids are endosymbiotic, including pathogenic forms and parasites.
Many protists move and feed by amoeboid behavior, but many of them aren't closely related at all. Therefore, the term "amoebae" has no taxonomic value and is comparable with classifying organisms in e.g. "flying animals" or "four-legged animals".
Traditionally amoebae were divided into shelled (Testacea) and naked amoeboids (Gymnamoebae). These names were recognized taxonomic units to describe these Protozoa, but the use of new techniques like the electron microscope has dramatically changed our scope. An example is the common amoeba Korotnevella (Fig. 1).
In light microscopy it appears to be naked, without any visible covering (Fig. 1A), but electron microscopy reveals that the cell is densely covered with self secreted micro-scales (Fig. 1B).
Some amoeboids like Cochliopodium species have larger micro-scales that can easily be seen with a light microscope. A coating of micro-scales is flexible and protects the -slow moving- cell against predators. It's called a tectum.
Other amoeboids have developed a thickened cell membrane called pellicle or theca. There are also amoebae that build a kind of shell like snales do. Such shells or tests are made from collected materials from the environment or from self secreted scales or platelets or a combination of both.
The largest number of amoeboid organisms can be found with the phyla Amoebozoa and Cercozoa. They have by far the greatest biomass of any protist taxon in soil and are also abundant in every marine habitat. They prey on bacteria and other protists.
Cercozoa is a diverse, increasingly well characterized phylum of protists founded mainly on the basis of 18S rDNA phylogenies that revealed a phylogenetic relationship between a variety of gliding zooflagellates and filose amoebae and the plasmodiophorid plant parasites. This diversity of cercozoan body forms includes:
• filose testate amoebae,
• amoeboflagellate algae,
• zooflagellates with pseudopodia and siliceous scales,
• diverse parasites,
• naked reticulose amoebae,
• testate reticulose amoebae,
• colonial flagellates,
• planktonic swimming flagellates,
• numerous small gliding flagellates,
• soft-bodied amoeboflagellates,
• thecate or scaly amoeboflagellates with a marked groove or cleft,
• and even protists with axopodia.