Rhizaria

Taxobox
fossil_range = Neoproterozoic - Recent


image_width = 200px
image_caption = Live "Ammonia tepida" (Foraminifera)
domain = Eukaryota
regnum = Rhizaria
regnum_authority = Cavalier-Smith, 2002
subdivision_ranks = Phyla
subdivision =
Cercozoa
"Retaria"
:Foraminifera
:RadiolariaThe Rhizaria are a species-rich supergroup of protists. They vary considerably in form, but for the most part they are amoeboids 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 with tubular cristae. There are three main groups of Rhizaria:

Cercozoa - Various amoebae and flagellates, usually with filose pseudopods and common in soil

Foraminifera - Amoeboids with reticulose pseudopods, common as marine benthos

Radiolaria - Amoeboids with axopods, common as marine plankton

A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea, parasites of plants and animals respectively, and the peculiar amoeba "Gromia". 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 in 2002, who also included the centrohelids and Apusozoa.

Evolutionary relationship

Rhizaria is part of the bikont clade, which also comprises the Archaeplastida, the Chromalveolata, the Excavata, and some smaller, unresolved groups such as the Apusozoa and the Centrohelida. As bikonts, they all descend from a heterotrophic eukaryote with two flagella.

Historically, many rhizarians were considered animals, 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, 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.

References

* cite journal
first = Thomas
last = Cavalier-Smith
authorlink = Thomas Cavalier-Smith
title = The phagotrophic origin of eukaryotes and phylogenetic classification of Protozoa
journal = International Journal of Systematic and Evolutionary Microbiology
year = 2002 | volume = 52 | issue = 2 | pages = 297–354
issn = 1466-5026
url = http://ijs.sgmjournals.org/cgi/content/abstract/52/2/297
accessdate = 2007-06-08
pmid = 11931142

* cite journal
first = Sergey I.
last = Nikolaev
coauthors = Cédric Berney, José F. Fahrni, Ignacio Bolivar, Stephane Polet, Alexander P. Mylnikov, Vladimir V. Aleshin, Nikolai B. Petrov, and Jan Pawlowski
title = The twilight of the Heliozoa and rise of the Rhizaria, an emerging supergroup of amoeboid eukaryotes
journal = Proceedings of the National Academy of Sciences
year = 2004 | volume = 101 | pages = 8066–8071 | issue = 21
issn = 0027-8424
url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=419558&rendertype=abstract
accessdate = 2007-06-08
doi = 10.1073/pnas.0308602101
pmid = 15148395

* cite journal
first = Burki
last = Fabien
coauthors = Kamran Shalchian-Tabrizi, Marianne Minge, Åsmund Skjæveland, Sergey I. Nikolaev, Kjetill S. Jakobsen, Jan Pawlowski
title = Phylogenomics Reshuffles the Eukaryotic Supergroups
journal = PLoS ONE
year = 2007 | volume = 2 | pages = e790- | issue = 8
url = http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0000790
accessdate = 2008-01-24
doi = 10.1371/journal.pone.0000790

External links

* [http://www.unige.ch/sciences/biologie/biani/msg/Amoeboids/Rizharia.html Molecular Phylogeny of Amoeboid Protists - Tree of Rhizaria]