The alveolates are a major line of protists. There are three main groups, which are very divergent in form, but are now known to be close relatives based on various ultrastructural and genetic similarities: Typical phyla Rhodophyta (red algae) Chromista Heterokontophyta (heterokonts) Haptophyta Cryptophyta (cryptomonads) Alveolates Pyrrhophyta (dinoflagellates) Apicomplexa Ciliophora (ciliates) Excavates Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies Protists are a heterogeneous group of living things, comprising those eukaryotes which are neither animals, plants, or fungi. ...

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. Classes & Subclasses Class Karyorelictea Class Heterotrichea (e. ... Cilium - Wikipedia, the free encyclopedia /**/ @import /skins-1. ... Classes & subclasses Class Conoidasida    Gregarinasina    Coccidiasina Class Aconoidasida    Haemosporasina    Piroplasmasina The Apicomplexa are a large group of protozoa, characterized by the presence of an apical complex at some point in their life-cycle. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Classes Dinophyceae Noctiluciphyceae Syndiniophyceae The dinoflagellates are a large group of flagellate protists. ... Parasitic excavate (Giardia lamblia) Green alga (Chlamydomonas) Flagellates are cells with one or more whip-like organelles called flagella. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... Mitochondria are visible as thread-like structures in the light microscope. ...

The Apicomplexa and dinoflagellates are closer to each other than they are 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. They include free-living members in Oxyrrhis, Acrocoelus, Colpodella, and perhaps Colponema, and parasites in Perkinsus, Parvilucifera, Cryptophagus, and the ellobiopsids. Microtubules are protein structures found within cells. ... Perkinsus marinus is a prevalent pathogen of oysters, causing massive mortality in oyster populations. ...

Relationships between some of these the major groups were suggested during the 1980s, and between all three by Cavalier-Smith in 1991, and confirmed by a genetic study by Gajadhar et al. in 1991. The name Alveolata was introduced by Tom Cavalier-Smith in 1991. Some studies suggested the haplosporids, mostly parasites of marine invertebrates, might belong here but they lack alveoli and are now placed among the Cercozoa. Thomas Cavalier-Smith is a professor of evolutionary biology at the University of Oxford, and is winner of the International Prize for Biology 2004 and one of the most notable researchers concerning the relationships, development, and classification of eukaryotes. ... Genera Haplosporidiidae    Haplosporidium    Minchina    Urosporidium Paramyxidae    Marteilia    Paramartelia    Paramyxa The Ascetosporea are a group of protists that are parasites of animals, especially marine invertebrates. ... The Cercozoa are a group of protists, including most amoebae and flagellates that feed by means of filose pseudopods. ...

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 advanced groups, others argue the alveolates originally lacked them and possibly the dinoflagellates and Apicomplexa acquired them separately. The Chromista are a eukaryotic supergroup, which may be treated as a separate kingdom or included among the Protista. ... Chromalveolates are a hypothetical grouping of eukaryotes, comprising the Chromista and alveolates, suggested by Tom Cavalier-Smith. ...

References

• Gajadhar, A. A. et al. (1991). Ribosomal RNA sequences of Sarcocystis muris, Theilera annulata, and Crypthecodinium cohnii reveal evolutionary relationships among apicomplexans, dinoflagellates, and ciliates. Molecular and Biochemical Parasitology 45: 147-153.
• Cavalier-Smith, T. (1991). Cell diversification in heterotrophic flagellates. In The Biology of Free-living Heterotrophic Flagellates, ed. D.J. Patterson & J. Larsen. pp. 113-131. Oxford University Press.