Composite image of various members of this 'supergroup' - interestingly, the only supergroup of protists to have been identified using comparative molecular biology - all the other robust supergroups were distinguished by morphological features. This was added to the site by D. J. Patterson. Image copyright: D. J. Patterson, image used under license to MBL (micro*scope).
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From the collection
|Description of Alveolates: Circumscription: A significant group containing many species of algae and protozoa-both free-living and parasitic. Grouping suggested initially by the presence of the alveoli (see synapomorphy). Began to appear in discussions in the early 1980s; the grouping was confirmed by Gajadhar et al. (1991); the colloquial name was formally introduced into the literature by Cavalier-Smith. With three major subsets, the ciliates distinguished by nuclear dimorphism and cilia arranged in kinetics. The dinoflagellates mostly with nuclei with unusual condensed chromosomes, and the apicomplexa - a group dominated by intracellular and extracellular parasites but including the agent for malaria. Structurally very complex. Ultrastructural identity: Mitochondria tubulocristate, cell surface underlain by a system of abutting sacs-the alveoli. Dictyosomes often reduced. Contains several lineages each with discrete ultrastructural identities (i.e., ciliates, apicomplexa, and dinoflagellates). Group has various idiosyncrasies such as eyes, ingestion devices, cytoproct, and extrusomes. Flagella when present (whether as flagella or cilia) typically with at least one cross-striated fibrous root. Synapomorphy: Tubulocristate protists with cortical alveoli (cortical alveoli defined as abutting sacs without attached ribosomes and not contiguous with other membranous systems and that form a continuous layer under the plasma membrane broken only by penetration of ingestion and egestion organelles, extrusomes, etc.). Composition: Includes the Apicomplexa (inclusive of the predatory flagellates Acrocoelus, Colpodella, and the parasitic Perkinsus, which get from one host to another as swimming forms), the ciliates (Ciliophora), and the dinoflagellates. Some consider affinities with one other flagellate, Colponema. However, the identity of this genus and the alveolate nature of the subsurface sacs in this genus still need to be clarified. Haplosporidia also excluded as structural evidence does not support molecular insights of an affinity between these and the alveolates. |