Amoebae are protists (mostly single celled organisms) that move and feed by extending and moving the cytoplasm of their cell. The extensions are called pseudopodia. Some of the cells in our own bodies can make pseudopodia – there are blood cells that use them to capture and eat foreign bodies and debris. These images are of living organisms. Most have to be taken with a microscope because the organisms are small (about 20-100 µm, 1 µm = 1/1000 mm). Various devices are used to create contrast within the images.
Amoebae are pleomorphic – in that their chape changes as to move along and feed – and is shown in the second row of images. Amoebae come in a variety yet distinctive of forms, some of which (Heliozoa) are included on a different page. Some have a shell (are ‘testate’) or are ‘naked’.
The pictures begin with an array of ‘naked’ amoebae with broad rounded pseudopodia. These pseudopodia grow from the front of the cell, moving the organism forward. There may be many pseudopodia as in Chaos, or just one (Vanella and Thecamoeba). A time-lapse sequence of Vanell shows how an amoeba changes shape as it moves along.
Other features of the cells, especially in Thecamoeba, are the hyaline cap at the top of the advancing pseudopodium, a posterior crumpled uroid, one or more nuclei and one or more contractile vacuoles. The nucleus in Thecamoeba has chromatin aggregated on the inside surface of the nucleus, but the nmcleus of many (Vanella, Nuclearia, Arcella) contains a spherical nucleolus which seems to lie within a watery sac.
It is evident that not all amoebae have broad pseudopodia. Many pseudopodia are very thin (Nuclearia, Pompholyxopphrys), and in some cases form a branching network (Lecythium, Lieberkuehnia, and Corallomyxa). In the case of the slime mold Fuligo (also called the dog barf slime mold), the network is a large plasmodium that may extend many inches, and is much like a very large multinucleated cell.
With the filose organisms we encounter amoebae with shells. Some, like Cochliopodium and Pompholyxophrys, have little scales or beads adhering to the outside. Some shells are organic and have a honeycomb appearance (Arcella) or are made from very small particles of grit (Difflugia). Foraminifera have shells made from an array of chambers – illustrated with the shell of Ammonia.
Paulinella is included because it has cyanobacterium-derived symbiont that lives within the cell and behaving largely as chloroplasts.