Amoeboid - Thierry Karsenti

Heliozoan (Actinophrys sol)
Amoeboids are unicellular lifeforms that mainly consist of contractile vacuoles, a
nucleus, and cytoplasm as their basic structure. They move and feed by means of
temporary cytoplasmic projections, called pseudopods (false feet). They have
appeared in a number of different groups. Some cells in multicellular animals may be
amoeboid, for instance human white blood cells, which consume pathogens. Many
protists also exist as individual amoeboid cells, or take such a form at some point in
their life-cycle. The most famous such organism is Amoeba proteus; the name amoeba
is variously used to describe its close relatives, other organisms similar to it, or the
amoeboids in general.
[edit] Morphological categories
Amoeboids may be divided into several morphological categories based on the form
and structure of the pseudopods. Those where the pseudopods are supported by
regular arrays of microtubules are called actinopods, and forms where they are not are
called rhizopods, further divided into lobose, filose, and reticulose amoebae. There is
also a strange group of giant marine amoeboids, the xenophyophores, that do not fall
into any of these categories.
• Lobose pseudopods are blunt, and there may be one or several on a cell,
which is usually divided into a layer of clear ectoplasm surrounding more
granular endoplasm. Most, including Amoeba itself, move by the body mass
flowing into an anterior pseudopod. The vast majority form a monophyletic
group called the Amoebozoa, which also includes most slime moulds. A
second group, the Percolozoa, includes protists that can transform between
amoeboid and flagellate forms.
• Filose pseudopods are narrow and tapering. The vast majority of filose
amoebae, including all those that produce shells, are placed within the
Cercozoa together with various flagellates that tend to have amoeboid forms.
The naked filose amoebae comprise two other groups, the vampyrellids and
nucleariids. The latter appear to be close relatives of animals and fungi.
• Reticulose pseudopods are cytoplasmic strands that branch and merge to
form a net. They are found most notably among the Foraminifera, a large