World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0000062298
Reproduction Date:

Title: Alveolata  
Author: World Heritage Encyclopedia
Language: English
Subject: Algae, Apicomplexa, Flagellate, Spirotrich, Dinoflagellate, Polyploid, Tetrahymena, Heterotrich, Plagiopylida, Nassophorea
Publisher: World Heritage Encyclopedia


Temporal range: Ediacaran [1] - Recent
Ceratium furca
Scientific classification
Domain: Eukarya
Kingdom: Chromalveolata
Superphylum: Alveolata


The alveolates ("with cavities")[2] are a major superphylum of protists.


There are four phyla, which are very diverse in form, but are now known to be close relatives based on various ultrastructural and genetic similarities:

The genus Perkinsus may belong to another clade, Perkinsozoa, based on a number of molecular biological findings.[3]


The most notable shared characteristic is the presence of cortical alveoli, flattened vesicles packed into a continuous layer supporting the membrane, typically forming a flexible pellicle. In dinoflagellates they often form armor plates. Alveolates have mitochondria with tubular cristae and their flagella or cilia have a distinct structure.

The ancestors of this group appear to have been photosynthetic.[4]

Almost all sequenced mitochondrial genomes of ciliates and apicomplexia are linear.[5] The mitochondrial genome of Babesia microti is circular.[6] This species is also now known not to belong to either of the genera Babesia or Theileria and a new genus will have to be created for it.


The Apicomplexa and dinoflagellates may be more closely related to each other than to the ciliates. Both have plastids, and most share a bundle or cone of microtubules at the top of the cell. In apicomplexans this forms part of a complex used to enter host cells, while in some colorless dinoflagellates it forms a peduncle used to ingest prey. Various other genera are closely related to these two groups, mostly flagellates with a similar apical structure. These include free-living members in Oxyrrhis and Colponema, and parasites in Perkinsus, Parvilucifera, Rastrimonas and the ellobiopsids. In 2001, direct amplification of the rRNA gene in marine picoplankton samples revealed the presence of two novel alveolate linages, called group I and II.[7][8] Group I has no cultivated relatives, while group II is related to the dinoflagellate parasite Amoebophrya, which was classified until now in the Syndiniales dinoflagellate order.

Relationships between some of these the major groups were suggested during the 1980s, and a specific relationship between all three was confirmed in the early 1990s by genetic studies, most notably by Gajadhar et al.[9] Cavalier-Smith, introduced the formal name Alveolata in 1991,[10] although at the time he actually considered the grouping to be a paraphyletic assemblage, rather than a monophyletic group.

Some studies suggested the haplosporids, mostly parasites of marine invertebrates, might belong here but they lack alveoli and are now placed among the Cercozoa.


The development of plastids among the alveolates is uncertain. Cavalier-Smith proposed the alveolates developed from a chloroplast-containing ancestor, which also gave rise to the Chromista (the chromalveolate hypothesis). However, as plastids only appear in relatively derived (as opposed to ancestral) groups, others argue the alveolates originally lacked them and possibly the dinoflagellates and Apicomplexa acquired them separately.

It appears that the alveolates, the dinoflagellates and the heterokont algae acquired their plastids from a red algae suggesting a common origin of this organelle in all these clades.[11]


It seems likely that the common ancestor of this group was a myzocytotic predator with two heterodynamic flagella, micropores, trichocysts, rhoptries, micronemes, a polar ring and a coiled open sided conoid.[12] This ancestor also probably possessed a plastid but it is presently not clear whether it was photosynthetic. Furthermore it is not clear whether extant perkinsids or colpodellids have retained this organelle.

Given that the alveolates, the dinoflagellates and the heterokont algae acquired their plastids from a red algae[11] it seems likely that their ancestor was photosynthetic.

In most of the species in this clade the primary extrusosome is the rhoptry suggesting its presence in their common ancestor.

The most likely path of evolution of the parasitic Apicomplexa seems to be from colpodellid like predators, to archigregarine like parasites and then to completely intracellular forms.


External links

  • Tree of Life: Alveolates

Template:Eukaryota classification

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.