Domain: Eukaryota
Kingdom: Chromalveolata Superphylum: Alveolata Phylum: Apicomplexa Class: Conoidasida Order: Eucoccidiorida Suborder: Eimeriorina Family: Aggregatidae Genus: Aggregata |
Chromalveolates & Apicomplexans
As you know from the previous page, over a billion years ago a heterotrophic eukaryote engulfed a cyanobacterium, and the rest is history. However, still over a billion years ago, a suspected secondary endosymbiosis occurred, and a red alga was eaten by another unicellular protist[1]. Although traces of a red alga seem to be present in plasmids or plasmid genes in the nuclear DNA of some chromalveolates, not all of them can photosynthesize[1]. Among those that can't are the apicomplexans, nearly all of which are animal parasites[1]. For their chosen low lifestyle, the apex of their cells are armed with a complex of organelles (hence the name) that aid in penetrating host cells or tissues[1]. A. bathytherma is one of these apicomplexans.
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Life Cycle[1, p583 diagram] + [3]
Aggregata have a complex life cycle, not only having as many alternative phases as Porphyra, but also using two distinct species as hosts at different parts of the cycle.
The sexual phase occurs in the digestive tract of a celphalopod (including Vulcanoctopus hydrothermalis) infected with sporozoites where the parasite goes through a small cascade of phases (see diagram) that spawn by erupting from different kinds of cells, eventually forming gametocytes (this is not good for the octopus, and most of the digestive tissue of the octopus can be replaced by Aggregata[2]). The gametocytes fuse and form and form a zygote, which develops into an oocyst that contains 50 to 200 sporocysts, which each contain 14 to 17 sporozoites[2]. When the oocysts are ingested by a crustacean (presumably by eating the infected tissue, but oocysts may also be passed from the celphalopod in stools[3]), they burst open and release the sporozoites, which infect the digestive tract of the crustaceans too. The cycle can restart when the crustacean is eaten by another cephalopod, such as a hungry Vulcanoctopus. |
Diagram showing apicomplexan life cycle:
1) Zygote 2) Oocyst and sporozoites 3) Merozoites 4) Gametocytes " |
References
[1]Campbell & Reece, Biology, 8th Edition
[2]Gestal, C., Pascual, S., & Hochberg, F. (2010). Aggregata bathytherma sp. nov. (Apicomplexa:Aggregatidae), a new coccidian parasite associated with a deep-sea hydrothermal vent octopus. Diseases Of Aquatic Organisms, 91(3), 237-242. doi:10.3354/dao02264
[3]https://en.wikipedia.org/wiki/Aggregata#Life_cycle
[2]Gestal, C., Pascual, S., & Hochberg, F. (2010). Aggregata bathytherma sp. nov. (Apicomplexa:Aggregatidae), a new coccidian parasite associated with a deep-sea hydrothermal vent octopus. Diseases Of Aquatic Organisms, 91(3), 237-242. doi:10.3354/dao02264
[3]https://en.wikipedia.org/wiki/Aggregata#Life_cycle