Amoebozoa are a type of protist that is characterized by the presence
of pseudopodia which they use for locomotion and feeding.
LEARNING OBJECTIVE [ edit ]
Describe characteristics of Amoebozoa
KEY POINTS [ edit ]
Amoebozoa (amoebas) can live in either marine and fresh water or in soil.
Amoebozoa are characterized by the presence of pseudopodia, which are extensions that can be
either tube-like or flat lobes and are used for locomotion and feeding.
Amooebozoa can be further divided into subclassifications that include slime molds; these can be
found as both plasmodial and cellular types.
Plasmodial slime molds are characterized by the presence of large, multinucleate cells that have
the ability to glide along the surface and engulf food particles as they move.
Cellular molds are characterized by the presence of independent amoeboid cells during times
of nutrient abundancy and the development of a cellular mass, called a slug, during times of
nutrient depletion.
Archamoebae, Flabellinea, and Tubulinea are also groups of Amoebozoa; their defining
characteristics include: Archamoebae lack mitochondria; Flabellinea flatten during locomotion
and lack a shell and flagella; Tubulinea have a rough cylindrical form during locomotion with
cylindrical pseudopodia.
TERMS [ edit ]
sporangia
an enclosure in which spores are formed (also called a fruiting body)
plasmodium
a mass of cytoplasm, containing many nuclei, created by the aggregation of amoeboid cells of
slime molds during their vegetative phase
rhizaria
a species-rich supergroup of mostly unicellular eukaryotes that for the most part are amoeboids
with filose, reticulose, or microtubule-supported pseudopods
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Amoebozoa
Protists are eukaryotic organisms that are
classified as unicellular, colonial, or
multicellular organisms that do not have
specialized tissues. This identifying
property sets protists apart from other
organisms within the Eukarya domain.
The amoebozoans are classified as protists
with pseudopodia which are used in
locomotion and feeding. Amoebozoans
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live in marine environments, fresh water, or in soil. In addition to the defining pseudopodia,
they also lack a shell and do not have a fixed body. The pseudopodia which are
characteristically exhibited include extensions which can be tube-like or flat lobes, rather
than the hair-like pseudopodia of rhizarian amoeba . Rhizarian amoeba are amoeboids with
filose, reticulose, or microtubule-supported pseudopods and include the groups: Cercozoa,
Foraminifera, and Radiolaria and are classified as bikonts. The Amoebozoa include several
groups of unicellular amoeba-like organisms that are free-living or parasites that are
classified as unikonts. The best known and most well-studied member of this group is the
slime mold. Additional members include the Archamoebae, Tubulinea, and Flabellinea.
Pseudopodia structures
Amoebae with tubular and lobe­shaped pseudopodia, such as the ones seen under this microscope, would
be morphologically classified as amoebozoans.
Slime Molds
A subset of the amoebozoans, the slime molds, has several morphological similarities to fungi
that are thought to be the result of convergent evolution. For instance, during times of stress,
some slime molds develop into spore-generating fruiting bodies, similar to fungi.
The slime molds are categorized on the basis of their life cycles into plasmodial or cellular
types. Plasmodial slime molds are composed of large, multinucleate cells that move along
surfaces like an amorphous blob of slime during their feeding stage. Food particles are lifted
and engulfed into the slime mold as it glides along. Upon maturation, the plasmodium takes
on a net-like appearance with the ability to form fruiting bodies, orsporangia, during times of
stress . Haploid spores are produced by meiosis within the sporangia. These spores can be
disseminated through the air or water to potentially land in more favorable environments. If
this occurs, the sporesgerminate to form ameboid or flagellate haploid cells that can combine
with each other and produce a diploid zygotic slime mold to complete the life cycle.
Badhamia utricularis
Badhamia utricularis: an example of a plasmodial slime mold with the ability to form a fruiting body.
The cellular slime molds function as independent amoeboid cells when nutrients are
abundant . When food is depleted, cellular slime molds pile onto each other into a mass of
cells that behaves as a single unit called a slug. Some cells in the slug contribute to a 2–3millimeter stalk, drying up and dying in the process. Cells atop the stalk form an asexual
fruiting body that contains haploid spores. As with plasmodial slime molds, the spores are
disseminated and can germinate if they land in a moist environment. One representative
genus of the cellular slime molds is Dictyostelium, which commonly exists in the damp soil of
forests.
Plasmodial slime mold: Physarum polycephalum
Physarum polycephalum is an example of a cellular slime mold.
Archamoebae, Flabellinea, and Tubulinea
The Archamoebae are a group of Amoebozoa distinguished by the absence of mitochondria.
They include genera that are internal parasites or commensals of animals
(Entamoeba andEndolimax). A few species are human pathogens, causing diseases such as
amoebic dysentery. The other genera of archamoebae live in freshwater habitats and are
unusual among amoebae in possessing flagella. Most have a single nucleus andflagellum, but
the giant amoeba, Pelomyxa, has many of each. The Tubulinea are a major grouping of Amoebozoa, including most of the larger and more
familiar amoebae like Amoeba,Arcella, and Difflugia. During locomotion, most Tubulinea
have a roughly cylindrical form or produce numerous cylindrical pseudopods. Each cylinder
advances by a single central stream of cytoplasm, granular in appearance, and has no
subpseudopodia. This distinguishes them from other amoeboid groups, although in some
members this is not the normal type of locomotion.