Phylum Mastigophora Mastigophores are the most primitive type of protozoans. They often have many flagella, and some are able to form pseudopodia. As discussed in Chapter Three, pseudopodia are finger-like extensions of the cytoplasm which can be used to surround engulf food particles or for movement. Mastigophores usually reproduce asexually through mitosis, although some varieties can reproduce sexually. They are usually parasitic; that is, they live inside another organism (the host organism) to obtain nutrients and in effect harm the host organism. However, some mastigophores are free-living, but since most are not, they are not used in the Simulation.
Phylum Sarcodina The sarcodines are a much more familiar group of protists than the mastigophores.
The most well-known example of a sarcodine is the famous amoeba. Lacking any rigid structure outside of their cell membrane, sarcodines can freely change their shape and form pseudopodia. Sarcodines can live in both freshwater and marine environments. They can reproduce both asexually and sexually, and they are usually free-living. Like mastigophores, sarcodines use pseudopodia to move and capture food.
Although the amoeba is generally thought of as lacking any structure, some have shells, and most other types of sarcodines also have shells. One class of sarcodines, the foraminiferans, possess calcareous shells (they are made of CaCO3).
Radiolarians also have shells, but theirs contain silica. While the latter two groups usually live in saltwater environments, the heliozoans live in freshwater. They too can have shells which contain silica.