Section II. CLASS RHIZOPODA
Members of this class include protozoans which use pseudopodia (false feet) for
locomotion. There are many species of this class that are free living and therefore will
not be discussed here. The attention is focused instead on those organisms which are
parasites of man. There are six genera recognized as human parasites. These include
the pathogens: Entamoeba histolytica and Naegleria fowleri, and some species of the
genera AcanthamoTba and Hartmanella, as well as commensal organisms from the
genera: Entamoeba, Endolimax, and lodamoeba. One commensal amoeba,
Entamoeba gingivalis, is found in the mouth of mammals.
LOCOMOTION AND DIGESTION
Locomotion and ingestion are accomplished by the use of the pseudopodia.
Once the food substance is contained within the cell, the organism goes through the
processes of enzymatically breaking down and absorbing the nutrients. Egestion of
unused residue is performed by the expulsion of the vacuole out of the cell.
RESPIRATION AND REPRODUCTION
Respiration is performed by simple absorption of dissolved oxygen from the liquid
environment. Excretion of gases and waste is performed by diffusion out of the
organism through the cell membrane. Liquid regulation inside the body is controlled by
contractile vacuoles which serve as two-way pumps that control the hydrostasis
between the organism and the environment. These organisms reproduce through
asexual reproduction consisting of simple cell division.
The amoebic organisms exist in two states. The vegetative state is called the
trophozoite. This is the metabolic stage of the protozoan which is very sensitive to the
changes of the environment. As unfavorable conditions set in, the organisms go
through a process called encystation. The cyst is the resistant state or stage of the
amoebic organisms. Excystation takes place with the return of favorable conditions.
Some species in this class also use the encystation process for the purpose of
reproduction. In this case one cyst yields more than one organism. See figure 1-3.