Sarcodina

Amoeboids are cells that move or feed by means of temporary projections, called pseudopods or false feet. They have appeared among a number of different groups. Some cells in animals may be amoeboid, such as white blood cells. Many protists take the form of individual amoeboid cells, or take such a form at some stage in their life-cycle.

Amoeboid protozoa may be organized into several broad categories, based on what type of pseudopods they form:

• Protozoa with lobose (blunt) or filose (tapering) pseudopods are called amoebae, although that term is sometimes used for any amoeboid. There are several different groups, found in various aqueous habitats and as parasites of other organisms. They also include the slime moulds.

• Nearly all protozoa with reticulose pseudopods, i.e. cytoplasmic strands that branch and merge to form a net, belong to a single group called the Foraminifera. These are mostly marine benthos that produce multichambered shells, and together with the radiolaria are the most important fossil protozoa.

• Protozoa with long, rigid pseudopods supported by microtubules are called actinopods. These are divided into the radiolaria, mostly marine plankton that produce intricate mineral skeletons, and heliozoa, protozoa found in both fresh and saltwater with at most simple skeletal elements like spines or spicules.

• The xenophyophores are strange benthic amoeboids that do not fit into any of the above categories. These may reach up to 20 cm in diameter.

Traditionally the amoeboid protozoa were grouped together as the Sarcodina, ranked variously as a class or phylum, with the above groups treated as formal taxa. However, since these categories are all based on form rather than phylogeny, newer systems separated them out and finally abandoned the Sarcodina altogether. They are now classified in various different groups, but as with most other protists, no solid consensus has been reached yet.