The most notable shared characteristic is the presence of cortical (outer-region) alveoli (sacs). These are flattened vesicles (sacs) packed into a continuous layer just under the membrane and supporting it, typically forming a flexible pellicle (thin skin). In dinoflagellates they often form armor plates. Alveolates have mitochondria with tubular cristae (ridges), and their flagellae or cilia have a distinct structure.
Almost all sequenced mitochondrial genomes of ciliates and apicomplexia are linear. The mitochondrial genome of Babesia microti is circular. 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.
Alveolata comprises around 9 major and minor groups, which are very diverse in form, and are known to be related by various ultrastructural and genetic similarities:
The Acavomonidia and Colponemidia were previously grouped together as colponemids, a taxon now split based on ultrastructural analysis. The Acavomonidia are closer to the dinoflagellate/perkinsid group than the Colponemidia are. As such, the informal term "colponemids", as it stands currently, covers two non-sister groups within Alveolata: the Acavomonidia and the Colponemidia.
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. 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 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. Cavalier-Smith introduced the formal name Alveolata in 1991, although at the time he actually considered the grouping to be a paraphyletic assemblage, rather than a monophyletic group.
Recent research indicates that the Dinoflagelllata actually emerged in the Perkinsea. Furthermore the Perkinsea emerged in the Apicomplexa.
Alveolata Cavalier-Smith 1991 [Alveolatobiontes]
The development of plastids among the alveolates is intriguing. Cavalier-Smith proposed the alveolates developed from a chloroplast-containing ancestor, which also gave rise to the Chromista (the chromalveolate hypothesis). Other researchers have speculated that the alveolates originally lacked plastids and possibly the dinoflagellates and Apicomplexa acquired them separately. However, it now appears that the alveolates, the dinoflagellates, the Chromerida and the heterokont algae acquired their plastids from a red alga with evidence of a common origin of this organelle in all these four clades.
A Bayesian estimate places the evolution of the alveolate group at ~ The Alveolata consist of Myzozoa, Ciliates, and Colponemids. In other words, the term Myzozoa, meaning "to siphon the contents from prey", may be applied informally to the common ancestor of the subset of alveolates that are neither ciliates nor colponemids. Predation upon algae is an important driver in alveolate evolution, as it can provide sources for endosymbiosis of novel plastids. The term Myzozoa is therefore a handy concept for tracking the history of the alveolate phylum..
The ancestors of the alveolate group may have been photosynthetic. The ancestral alveolate probably possessed a plastid. Chromerids, apicomplexans, and peridinin dinoflagellates have retained this organelle. Going one step even further back, the chromerids, the peridinin dinoflagellates and the heterokont algae possess a monophyletic plastid lineage in common, i.e. acquired their plastids from a red alga, and so it seems likely that the common ancestor of alveolates and heterokonts was also photosynthetic.
In one school of thought the common ancestor of the dinoflagellates, apicomplexans, Colpodella, Chromerida, and Voromonas was a myzocytotic predator with two heterodynamic flagella, micropores, trichocysts, rhoptries, micronemes, a polar ring and a coiled open sided conoid. While the common ancestor of alveolates may also have possessed some of these characteristics, it has been argued that Myzocytosis was not one of these characteristics, as ciliates ingest prey by a different mechanism.
An ongoing debate concerns the number of membranes surrounding the plastid across apicomplexans and certain dinoflagellates, and the origin of these membranes. This ultrastructural character can be used to group organisms and if the character is in common, it can imply that phyla had a common photosynthetic ancestor. On the basis that apicomplexans possess a plastid surrounded by 4 membranes, and that peridinin dinoflagellates possess a plastid surrounded by 3 membranes, Petersen et al. have been unable to rule our that the shared stramenopile-alveolate plastid could have been recycled multiple times in the alveolate phylum, the source being stramenopile-alveolate donors, through the mechanism of ingestion and endosymbiosis.
Ciliates are a model alveolate, having been genetically studied in great depth over the longest period of any alveolate lineage. They are unusual among eukaryotes in that reproduction involves a micronucleus and a macronucleus. Their reproduction is easily studied in the lab, and made them a model eukaryote historically. Being entirely predatory and lacking any remnant plastid, their development as a phylum illustrates how predation and autotrophy are in dynamic balance and that the balance can swing one way or other at the point of origin of a new phylum from mixotrophic ancestors, causing one ability to be lost.
Adelina is a genus of alveolates within the phylum Apicomplexa. They are coccidian parasites of arthropods and oligochaetes. Host orders include Coleoptera, Diptera, Collembola, Embioptera, Lepidoptera and Orthoptera.Angeiocystis
Angeiocystis is a genus of parasitic alveolate eukaryotes belonging to the phylum Apicomplexa.Caryospora (alveolate)
Caryospora is a genus of parasitic protozoa in the phylum Apicomplexa. The species in this genus infect birds and reptiles with the majority of described species infecting snakes. It is the third largest genus in the family Eimeriidae.
Despite the number of species in this genus, it has not been much studied.Chromerida
Chromerida is a phylum of unicellular alveolates, which includes photosynthetic species Chromera velia and Vitrella brassicaformis. General features of the phylum include spherical cells each with a thick cell wall, chloroplast present with chlorophyll a only (no chlorophyll b or c), and an internal developing flagellum at some lifestages.
They often live in close association with corals, and studies suggest their closest relatives is the parastic group Apicomplexa, which evolved from photosyntethic ancestors, making Chromerida the last remaining photosynthetic members of an otherwise parasitic branch within Alveolata.Carter Lab at University of Sydney has undertaken new experiments to isolate novel Chromerids, using the same methods that were used to isolate Chromera velia and Vitrella brassicaformis. These methods were agreed at the First Chromera Conference and Workshop held at the Heron Island Research Station, Queensland, Australia from November 21–25, 2011.Colpodellida
Colpodellida is an order of alveolate eukaryotes, which includes small predatory species such as Colpodella pugnax.Diaspora (Apicomplexa)
Diaspora is a genus in the phylum Apicomplexa, first described by Leger in 1898.Duboscquella
Duboscquella is a genus of dinoflagellates.Garnia (Apicomplexa)
Garnia is a genus of parasitic alveolates belonging to the phylum Apicomplexia.Haemoproteus plataleae
Haemoproteus plataleae is a species of parasitic alveolate eukaryotes that infects ibises and spoonbills. It has been recovered from adult and juvenile American white ibises in Florida.Ithania wenrichi
Ithania is a genus of parasitic alveolates of the phylum Apicomplexa.
This genus was described in 1947 by Ludwig.Lankesterella (Apicomplexa)
Lankesterella is a genus in the phylum Apicomplexa. Species in this genus infect amphibians.The type species is Lankesterella minima.Merogregarina
Merogregarina is a genus of parasitic alveolate in the phylum Apicomplexa. Species in this genus infect marine invertebrates.Myriospora (Apicomplexa)
Myriospora is a genus of parasitic alveolates belonging to the phylum Apicomplexa.Myzocytosis
Myzocytosis (from Greek: myzein, (μυζεῖν) meaning "to suck" and kytos (κύτος) meaning "container", hence referring to "cell") is a method of feeding found in some heterotrophic organisms. It is also called "cellular vampirism" as the predatory cell pierces the cell wall and/or cell membrane of the prey cell with a feeding tube, the conoid, sucks out the cellular content and digests it.
Myzocytosis is found in Myzozoa and also in some species of Ciliophora (both comprise the alveolates). A classic example of myzocytosis is the feeding method of the infamous predatory ciliate, Didinium, where it is often depicted devouring a hapless Paramecium. The suctorian ciliates were originally thought to have fed exclusively through myzocytosis, sucking out the cytoplasm of prey via superficially drinking straw-like pseudopodia. It is now understood that suctorians do not feed through myzocytosis, but actually, instead, manipulate and envenomate captured prey with their tentacle-like pseudopodia.Myzozoa
Myzozoa is a grouping of specific phyla within Alveolata, that either feed through myzocytosis, or were ancestrally capable of feeding through myzocytosis.A large number of protozoan orders group within Myzozoa.It is sometimes described as a phylum, containing the major subphyla Dinozoa and Apicomplexa, plus minor subphyla.The term Myzozoa superseded the previous term "Miozoa", by the same authority, and gave a slightly altered meaning.Octosporella (Apicomplexa)
Octosporella is a genus in the phylum Apicomplexa. This genus has been poorly studied and little is known about it.
Species in this genus infect fish, lizards and echidnas.Stentor (ciliate)
Stentor, sometimes called trumpet animalcules, are a genus of filter-feeding, heterotrophic ciliates, representative of the heterotrichs. They are usually horn-shaped, and reach lengths of two millimeters; as such, they are among the biggest known extant unicellular organisms. They reproduce asexually through binary fission.Telonema
Telonema is a genus of single-celled organisms.
Some sources group Telonema within the cryptomonads-haptophytes assemblage. It is sometimes assigned to a unique phylum, Telonemia. Although Telonema is within the Eukaryota Domain, it does not have any close relations to other organisms within that domain . However, it was once thought Telonema was closely related to photosynthetic cryptomonads, or stramenopiles and centrohelids, but their wasn't enough data to prove this. After a study of 127 genes was done across 72 species, they found that Telonema Subtilis could be related to alveolate, and rhizaria.Voromonas
Voromonas is a genus of predatory alveolates. The genus and species were described by Mylnikov in 2000. It was originally described as Colpodella pontica but was renamed by Cavalier-Smith and Chao in 2004.