Rhizaria

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Rhizaria

The Rhizaria are a species-rich supergroup of protist

Protist

Protists ; eukaryote microorganisms. Historically, protists were treated as the kingdom Protista but this group is no longer recognized in modern taxonomy....
s. They vary considerably in form, but for the most part they are amoeboid

Amoeboid

Amoeboids are unicellular life-forms characterized by their similarity to amoebas....
s with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have mitochondria

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
with tubular cristae.

e are three main groups of Rhizaria:

A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera.

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Encyclopedia

The Rhizaria are a species-rich supergroup of protist

Protist

Amoeboid

Mitochondrion

In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryote cell . These organelles range from 0.5–10 micrometers in diameter....
with tubular cristae.

Groups

There are three main groups of Rhizaria:

Cercozoa
Cercozoa

The Cercozoa are a group of protists, including most amoeboids and flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome or mouth as found in many other protozoa....
- Various amoebae and flagellates, usually with filose pseudopods and common in soil

Foraminifera
Foraminifera

The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net....
- Amoeboids with reticulose pseudopods, common as marine benthos
Benthos

Benthos are the organisms which live on, in, or near the seabed, also known as the benthic zone. They live in or near marine sedimentary environments, from tidal pools along the Intertidal zone, out to the continental shelf, and then down to the Abyssal zone....

Radiolaria - Amoeboids with axopods, common as marine plankton
Plankton

Plankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their Phylogenetics or taxonomy classification....

A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the Phytomyxea

Phytomyxea

The Phytomyxea are a group of protists that are parasites of plants. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa....
and Ascetosporea

Ascetosporea

The Ascetosporea are a group of protists that are parasites of animals, especially marine invertebrates. There are two groups, the haplosporids and paramyxids, which are not particularly similar morphologically but consistently group together on molecular trees, which place them near the base of the Cercozoa....
, parasites of plants and animals respectively, and the peculiar amoeba Gromia
Gromia

Gromia is a widespread genus of marine and freshwater amoeboids, closely resembling some foraminiferans. It produces an organic test, which is ovoid or lobed and may exceed one millimetre in size; this resembles a small grape, in that its centre is fluid-filled but lacks organic matter, which is concentrated in its translucent test and u...
. The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith

Thomas Cavalier-Smith

Professor Thomas Cavalier-Smith , Royal Society, Royal Society of Canada, Natural Environment Research Council Professorial Fellow, is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford....
in 2002, who also included the centrohelid

Centrohelid

The centrohelids or centroheliozoa are a large group of heliozoan protists. They include both mobile and sessile forms, found in freshwater and marine environments, especially at some depth....
s and Apusozoa

Apusozoa

The Apusozoa comprise several genera of flagellate protozoa. They are usually around 5-20 ?m in size, and occur in soils and aquatic habitats, where they feed on bacterium....
.

Evolutionary relationship

Rhizaria is part of the bikont

Bikont

A Bikont is a eukaryote cell with two flagella, as its name suggests. It is a division of eukaryotes....
clade

Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article in the conventional sense of "an a...
, which also comprises the Archaeplastida

Archaeplastida

The Archaeplastida or Primoplantae are a major line of eukaryotes, comprising the embryophytes, green alga and red algae, and a small group called the glaucophytes....
, the Chromalveolata, the Excavata, and some smaller, unresolved groups such as the Apusozoa

Apusozoa

The Apusozoa comprise several genera of flagellate protozoa. They are usually around 5-20 ?m in size, and occur in soils and aquatic habitats, where they feed on bacterium....
and the Centrohelid

Centrohelid

Heterotroph

A heterotroph is an organism that organic compound substrates to get its Energy#Chemical energy for its life cycle. This contrasts with autotrophs such as plants which are able to directly use sources of energy such as light to produce organic substrates from inorganic carbon dioxide....
ic eukaryote with two flagella.

Historically, many rhizarians were considered animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the Kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life....
s, with their motility and heterotrophy as justification. However, when the five-kingdom system took prevalence over the animal-plant dichotomy, the rhizarians were put into the kingdom Protista. Then, after Woese published his three-domain system, because of the paraphyly of the kingdom Monera

Monera

Monera are bacteria and other mostly tiny, single-celled organisms whose genetic material is loose in the cell. The genetic material of plants, animals, and other eukaryotes , on the other hand, is held in the cell's nucleus....
, taxonomists turned their attention to the eukaryote domain, and the inherent paraphyly of Protista. After much debate, which continues to this day, Rhizaria emerged as a monophyletic group.

Rhizaria

Groups

Evolutionary relationship

External links