Amoebozoa - Morphology

Morphology

The cell is typically divided into a granular central mass, called endoplasm, and a clear outer layer, called ectoplasm. During locomotion the endoplasm flows forwards and the ectoplasm runs backwards along the outside of the cell. Many amoeba move with a definite anterior and posterior; in essence the cell functions as a single pseudopod. They usually produce numerous clear projections called subpseudopodia (or determinate pseudopodia), which have a defined length and are not directly involved in locomotion.

Other amoebozoans may form multiple indeterminate pseudopodia, which are more or less tubular and are mostly filled with granular endoplasm. The cell mass flows into a leading pseudopod, and the others ultimately retract unless it changes direction. Subpseudopodia are usually absent. In addition to a few naked forms like Amoeba and Chaos, this includes most amoebae that produce shells. These may be composed of organic materials, as in Arcella, or of collected particles cemented together, as in Difflugia, with a single opening through which the pseudopodia emerge.

The primary mode of nutrition is by phagocytosis: the cell surrounds potential food particles, sealing them into vacuoles where the may be digested and absorbed. Some amoebae have a posterior bulb called a uroid, which may serve to accumulate waste, periodically detaching from the rest of the cell. When food is scarce, most species can form cysts, which may be carried aerially and introduce them to new environments. In slime moulds, these structures are called spores, and form on stalked structures called fruiting bodies or sporangia.

Most Amoebozoa lack flagella and more generally do not form microtubule-supported structures except during mitosis. However, flagella occur among some archamoebae, and many slime moulds produce biflagellate gametes. The flagellum is generally anchored by a cone of microtubules, suggesting a close relationship to the opisthokonts. The mitochondria characteristically have branching tubular cristae, but have been lost among archamoebae.