View source for Chromalveolate

{{taxobox
| color = greenyellow
| name = Chromalveolate
| image =
| image_width = 225px
| image_caption = ''[[Ceratium hirundinella]]'', a [[dinoflagellate]]
| image2 = Chromista collage 2.jpg
| image2_width = 300px
| image2_caption = Clockwise from top-left: a [[haptophyte]], some [[diatom]]s, a [[water mold]], a [[cryptomonad]], and ''[[Macrocystis]]'', a [[phaeophyte]]
| domain = [[Eukarya]]
{{Taxobox_norank_entry | taxon = [[Bikonta]]}}
| unranked_regnum = [[Corticata]]
| regnum = '''Chromalveolata'''[[paraphyly|*]]
| subdivision_ranks = Phyla
| subdivision = *[[Heterokont]]ophyta
*[[Haptophyta]]
*[[Cryptophyta]]
*'''[[Alveolata]]''' (Superphylum)
**[[Ciliophora]]
**[[Apicomplexa]]
**[[Dinoflagellata]]
}}

'''Chromalveolata''' is a [[eukaryote]] supergroup first proposed by [[Thomas Cavalier-Smith]] as a refinement of his [[kingdom (biology)|kingdom]] [[Chromista]], which was first put forward in 1981.  Chromalveolata was proposed to represent the result of a single secondary [[endosymbiosis]] between a line descending from a [[bikont]] and a [[red alga]]<ref name="pmid19335769">{{cite journal |author=Keeling PJ |title=Chromalveolates and the evolution of plastids by secondary endosymbiosis |journal=J. Eukaryot. Microbiol. |volume=56 |issue=1 |pages=1–8 |year=2009 |pmid=19335769 |doi=10.1111/j.1550-7408.2008.00371.x }}</ref> that became the progenitor of [[chlorophyll c]] containing [[plastid]]s. In a major classification produced in 2005, Chromalveolata was regarded as one of the six major groups within the eukaryotes.<ref name=Adl2005>
 {{cite
 | first = Sina M. 
 | last = Adl
 | coauthors = ''et al.''
 | title = The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists
 | journal = Journal of Eukaryotic Microbiology
 | year=2005 | volume=52 | issue=5 | pages=399
 | url=http://www.blackwell-synergy.com/doi/abs/10.1111/j.1550-7408.2005.00053.x
 | doi = 10.1111/j.1550-7408.2005.00053.x
}}
</ref> However this has been increasingly challenged. Thus two papers published in 2008 have phylogenetic trees in which the chromalveolates are split up.<ref name=Burki2008a>{{Cite journal |last=Burki |first=Fabien |last2=Shalchian-Tabrizi |first2=Kamran |last3=Pawlowski |first3=Jan |year=2008 |title=Phylogenomics reveals a new 'megagroup' including most photosynthetic eukaryotes |journal=Biology Letters |volume=4 |pages=366–369 |doi=10.1098/rsbl.2008.0224 |lastauthoramp=yes |pmid=18522922 |issue=4 |pmc=2610160 |postscript=<!--None--> }}</ref><ref name=KimGraham2008>{{cite journal | doi = 10.1371/journal.pone.0002621 | year = 2008 | month = Jul | author = Kim, E; Graham, LE | title = EEF2 analysis challenges the monophyly of Archaeplastida and Chromalveolata. | volume = 3 | issue = 7 | pages = e2621 | pmid = 18612431 | pmc = 2440802 | journal = PLoS ONE | url = http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002621 | format = Free full text }}</ref>

==Groups and classification==
Historically, many chromalveolates were considered [[plant]]s, because of their cell walls, photosynthetic ability, and in some cases their morphological resemblance to the land plants ([[Embryophyta]]).  However, when the five-kingdom system took prevalence over the animal-plant dichotomy, most chromalveolates were put into the kingdom [[Protista]], with the [[water mold]]s and [[Labyrinthulomycetes|slime nets]] put into the kingdom [[Fungi]], and the [[brown algae]] staying in the plant kingdom.

In 2005, in a classification reflecting the consensus at the time, the Chromalveolata were regarded as one of the six major [[clade]]s of eukaryotes.<ref name=Adl2005/> Although not given a formal taxonomic status in this classification, elsewhere the group has been treated as a Kingdom. The Chromalveolata were divided into four major subgroups:

* [[Cryptophyta]]
* [[Haptophyta]]
* [[Stramenopiles]] (or Heterokontophyta)
* [[Alveolata]]

Other groups which may be included within, or related to, chromalveolates, are:
*[[Telonemia]]<ref>{{cite journal | author = Shalchian-Tabrizi K, Eikrem W, Klaveness D, Vaulot D, Minge M, Le Gall F, Romari K, Throndsen J, Botnen A, Massana R, Thomsen H, Jakobsen K | title = Telonemia, a new protist phylum with affinity to chromist lineages | journal = Proc Biol Sci | volume = 273 | issue = 1595 | pages = 1833–42 | year = 2006 | pmid = 16790418 | pmc = 1634789 | doi = 10.1098/rspb.2006.3515}}</ref>

Though several groups, such as the [[ciliate]]s and the [[water mold]]s, have lost the ability to photosynthesize, most are [[autotroph]]ic.  All photosynthetic chromalveolates use [[chlorophyll]]s ''a'' and ''c'', and many use accessory pigments. Chromalveolates share similar [[glyceraldehyde 3-phosphate dehydrogenase]] proteins.<ref name="pmid19270733">{{cite journal |author=Takishita K, Yamaguchi H, Maruyama T, Inagaki Y |title=A hypothesis for the evolution of nuclear-encoded, plastid-targeted glyceraldehyde-3-phosphate dehydrogenase genes in "chromalveolate" members |journal=PLoS ONE |volume=4 |issue=3 |pages=e4737 |year=2009 |pmid=19270733 |pmc=2649427 |doi=10.1371/journal.pone.0004737 |url=http://dx.plos.org/10.1371/journal.pone.0004737}}</ref>

However, as early as 2005, doubts were being expressed as to whether the Chromalveolata was monophyletic,<ref>Harper, J. T., Waanders, E. & Keeling, P. J. 2005. On the monophyly of chromalveolates using a six-protein phylogeny of eukaryotes. Int. J. System. Evol. Microbiol., 55, 487-496. [http://www.botany.ubc.ca/keeling/PDF/05chromalvJSEM.pdf]</ref> and a review in 2006 noted the lack of evidence for several of the supposed six major eukaryote groups, including the Chromalveolata.<ref name="parfrey">{{cite journal | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1713255 | title = Evaluating Support for the Current Classification of Eukaryotic Diversity | author = Laura Wegener Parfrey, Erika Barbero, Elyse Lasser, Micah Dunthorn, Debashish Bhattacharya, David J Patterson, and Laura A Katz | doi = 10.1371/journal.pgen.0020220 | journal = PLoS Genet. | date = 2006 December | volume = 2 | issue = 12 | pages = e220 | pmid = 17194223 | pmc = 1713255 }}</ref>. {{As of|2010}} there seems to be an emerging consensus that the group is not monophyletic. The four original subgroups fall into two categories, one comprising the Cryptophyta and the Haptophyta, the other the Stramenopiles and the Alveolata.<ref name=Burki2008a/><ref name=KimGraham2008/> 

===Halvaria===
{{main|Halvaria}}
Analyses in 2007 and 2008 agree that the Stramenopiles and the Alveolata are related, forming a reduced chromalveolate clade.

===Hacrobia===
{{main|Hacrobia}}
The [[Haptophyta]] and [[Cryptophyta]] are related in these analyses,<ref name=Burki2008a/><ref name=KimGraham2008/> forming a clade which has been called 'Hacrobia'.

===Position of SAR and Hacrobia===

The Hacrobia appear to be more closely related to the [[Archaeplastida]] (plants in the very broad sense), being a sister group in one analysis,<ref name=Burki2008a/> and actually nested inside this group in another.<ref name=KimGraham2008/> (Earlier, [[Cavalier-Smith]] had suggested a clade called [[Corticata]] for the grouping of ''all'' the chromalveolates and the Archaeplastida.<ref>{{cite pmid|11931142}}</ref>) The SAR supergroup and the Archaeplastida/Hacrobia combination are grouped in the [[bikont]]s, which all appear to descend from a heterotrophic eukaryote with two flagella.

==Morphology==
Chromalveolates, unlike other groups with multicellular representatives, do not have very many common morphological characteristics.  Each major subgroup has certain unique features, including the alveoli of the Alveolata, the haptonema of the Haptophyta, the ejectisome of the Crytophyta, and the two different flagella of the Heterokontophyta.  However, none of these features are present in all of the groups.

The only common chromalveolate features are these:
*The shared origin of chloroplasts, as mentioned above
*Presence of [[cellulose]] in most cell walls

Since this is such a diverse group, it is difficult to summarize shared chromalveolate characteristics.

==Ecological role==
[[Image:symptom potato late blight.jpg|right|thumb|A potato plant infected with ''[[Phytophthora infestans]]''.]]
Many chromalveolates affect our ecosystem in enormous ways.  Some of these organisms can be very harmful.  [[Dinoflagellate]]s produce [[red tide]]s which can devastate fish populations and intoxicate oyster harvests.  [[Apicomplexan]]s are some of the most successful specific parasites to animals.  Water molds cause several plant diseases.  In fact, it was a water mold, ''[[Phytophthora infestans]]'', that caused the [[Great Irish Famine|Irish potato famine]].
[[Image:Kelp forest.jpg|thumb|left|A [[California]]n kelp forest.]]  

However, many chromalveolates are vital members of our ecosystem.  [[Diatom]]s are one of the major photosynthetic producers, and as such produce much of the [[oxygen]] we breathe, and also take in much of the [[carbon dioxide]] from the atmosphere.  [[Brown algae]], most specifically [[kelp]]s, create underwater "forest" habitats for many marine creatures, and provide a large portion of the diet of coastal communities.

Chromalveolates also provide many products that we use.  The [[algin]] in brown algae is used as a food thickener, most famously in [[ice cream]].  The siliceous shells of diatoms have many uses, such as in reflective paint, in toothpaste, or as a filter, in what is known as [[diatomaceous earth]].
{{-}}

== References ==
{{reflist|2}}

== External links ==
* [http://tolweb.org/Eukaryotes/3 Tree of Life Eukaryotes]

{{Life}}
{{Heterokont}}
{{Alveolata}}
{{Cryptophyta and haptophyta}}

[[Category:Eukaryotes]]
[[Category:Chromalveolata]]

[[ar:أسناخ صبغية]]
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[[ja:クロムアルベオラータ]]
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