Biomedical Engineering Reference
In-Depth Information
Opisthokonta
Choanozoa (Chapter 23)
Animalia (Chapters 25
32)
Fungi (Chapters 33
37)
Class Eukaryota is broadly divided into two large domains, the Bikonta (two
flagella) and the Unikonta (one flagellum). The Amoebozoa belong to the Class
Unikonta. Most extant Amoebozoa species have no flagella, but a few species
of amoebozoans retain their ancestral flagellum. Because the amoebozoans are
Unikonts, they are related to Class Opisthokonta (Chapters 23, 25
37), which
includes Class Choanozoa, Class Animalia, and Class Fungi.
Amoebozoa move by flowing their cytoplasm from one area of the cell to
another. Movement begins when a part of the cell wall, the lobopodium, is
protruded. As cytoplasm flows into the lobopodium, the rest of the cell cannot
help but follow. The amoebozoan genera vary greatly in size. Species producing
disease in humans are about the size of human cells (10
40 microns), while at
least one non-pathogenic species, Amoebozoa proteus, attains a size of 800
microns (on the verge of visibility with the unaided eye). The members of Class
Amoebozoa engulf and eat smaller organisms. Most members of Class
Amoebozoa live in the soil or aquatic environments, where they are beneficial
bacterial predators (Entamoeba is an exception, see below) [73]. The pathogenic
members of Class Amoebozoa occur in tissues as trophozoites (the amoeboid
feeding cells) or as cysts (round, infective cells resistant to desiccation).
Determining the major subclasses of Class Amoebozoa has proven to be
very difficult [82]. It is likely that the class schema shown in this chapter
will be changed in the next few years, when newly acquired genomic infor-
mation is studied along with previously documented morphologic and
physiologic data. In this topic, Class Amoebozoa is divided into two major
subclasses: Class Lobosea and Class Conosa. All of the pathogenic genera
within Class Lobosea are capable of producing meningoencephalitis. Class
Conosa includes one pathogenic genus: Entamoeba histolytica, which typi-
cally produces a dysentery-like condition. Aside from this division that
neatly distinguishes the primary infections of the central nervous system and
the primary infections of the intestines, the taxonomy of the infectious
Amoebozoans is best studied genus-by-genus.
Amoebozoa
Lobosea
Discosea
Thecamoebidae
*Sappinia
Centramoebida
Acanthamoebidae
*Acanthamoeba
*Balamuthia
