Amoebae are familiar creatures from introductory biology. We all think we know what they look like: shifting shapeless globs of slime. But a closer look can surprise us. They display a tremendous array of shapes and colors, and some species are capable of fairly complex behaviors.
Two morphological characters are used to distinguish the major types of amoebae: the form of their pseudopods, and the presence or absence of a hard covering (a “test”).
- Pseudopods are outgrowths of the cell that are used for locomotion, food capture, and other functions. They can be largely static, or highly mobile. The “classical” pseudopods, e.g. those of Amoeba proteus are tubular or sub-cylindrical. Pseudopods which are fine and thread-like are called filopodia.
- Tests can be formed by accumulating external debris (like sand grains and diatom frustules) or be made by the cell itself. They often take the form of scales or beads which are assembled into a shell-like outer covering, into which the amoeba can retreat.
Amoeboid motility displayed by most amoebae involve the adhesion of the cell to a surface and the streaming of cytoplasm, as displayed in the video below.