Sarcodina are single-celled organisms. Amoebas are members of the sarcodines.They may reproduce asexually or sexually. Asexual reproduction is a simple cell division, called fission, in which division of the genetic material can be seen in the nucleus or center of the cell. Free flowing sarcodines are amoebas. Not all amoebas cause illness, but those that do cause illnesses can cause such severe symptoms as brain swelling, digestive distress and even organ cysts. Sarcodines 'eat' by surrounding their food. This process is called 'phagocytosis'.
Sarcodines move with pseudopoda, or 'false feet.' The cytoplasm of the cell moves by extending itself in the direction that it wants to go. If the sarcodine has a skeleton, it is able to move by extensions of itself that extend beyond its shell, or it may also move on the extensions of the shell itself, called axial rods. Flagella, or external structures on the sarcodine are sometimes present during parts of the life cycle of the sarcodine, sometimes in the sexual cells of the sarcodine, or the gametes. Some sarcodines have a shell or covering called a test. Foraminiferans have tests made of calcium, and radiolarians have tests made out of silica. Occasionally this 'skeleton' may be internal to the creature.
The life cycle of the sarcodine may consist of a latent state as a cyst, and a working state as a "trophic," or growing and reproducing organism. This may occur in certain amoebas that cause illness, (such as in the amoeba that causes diarrhea).The 'cyst' state generally protects the amoeba from harsh conditions of the environment till it reaches the host. Illnesses caused by the sarcodine may include infection of the vagina, infection of the digestive tract, fever, infection of the skin, brain, organ systems, diarrhea and malaria.
In the cyst form, amoebas may enter the digestive tract (through unwashed hands or food). Other amoebic infections can be obtained by bathing in infected water, and may enter the body through the mucous membranes of the eyes, nose or genitals. Sarcodines which go through a larval stage are not at sexual maturity; they may, however, divide through fission. When they are at this stage, they may live in an animal called the "intermediate host." At sexual maturity, the organism is hosted by the "definitive host." "Free" amoebas do not need an intermediate host; they are immediately pathogenic, or able to cause infection to the host.
Asexual reproduction occurs in several ways. In fission, the cell is split into two cells that are roughly the same size. When a sarcodine produces a bud, the genetic material divides equally, but the cytoplasm of the newly formed organism is much smaller. However, the genetic material is necessary for the health of the sarcodine, because experiments have shown that cells cannot survive without it. In plasmotomy, the nucleus reproduces inside the single cell, and then the cell membrane divides the cell into several smaller cells, each containing several nuclei. In schizogony, the nucleus divides into several more nuclei, and then the new nuclei are contained in smaller cellular membranes than the original cell.
Sexual reproduction occurs when the amoeba separates the genetic material into half the number of chromosomes needed for an adult cell; this genetic stage is called 'haploid'. When sex cells of different amoebas combine, they become a genetically unique organism.