Haplosporidia
| Haplosporidia | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Haplosporidia | ||||||||||||
| Caullery & Mesnil , 1899 |
The Haplosporidia are a group of protozoa that live as endoparasites inside various aquatic animals. They are of economic importance as pathogens in mussel cultures. They systematically belong to the Rhizaria .
features
Life cycle
The Haplosporidia have a complex life cycle, which, however, is not completely elucidated in any of the species. Small amoeboid cells hatch from the spores in the host's digestive tract . These migrate into the connective tissue or into epithelia , where they grow into multinucleated plasmodia . The large plasmodia divide irregularly into smaller plasmodia with different numbers of nuclei . This cycle of division is repeated several times. The resulting plasmodia spread extracellularly in the tissue. At the beginning of the spore formation a cell wall forms around a large, multinucleated plasmodium , the plasmodium thus becomes a sporontium . This is where karyogamy is likely to occur, followed by meiosis . The remaining stages of the life cycle are all likely to be haploid . The spontaneous division later divides several times and forms mononuclear sporoblasts.
Another doctrine is that two haploid sporoblasts combine to form a diploid zygote , and the diploid stage is maintained over the rest of the life cycle. Which of the two assumptions is correct or whether both occur is not clear.
Two halves are formed from the sporoblast: the nucleated half, the episporoplasm, envelops the nucleated half, the sporoplasm, and separates from it through cell division. This creates a nucleated cell inside the vacuole of a nucleated cell. The episporoplasm now forms the spore wall and then degenerates. The spore wall includes a variety of species-specific ornamentation and at one end a flap with which the spore opens later.
The presence of intermediate hosts is suspected but has not been established.
Organelles
The haplosporidia have haplosporosomes on specific organelles . These are located in the cytoplasm of sporonts and sporoblasts. These are spherical, electron-dense vesicles surrounded by a plasmalemma with a diameter of 70 to 250 nm. They contain membranous structures and glycoproteins . Their function is unknown.
The spherulosomes are interpreted as descendants of the Golgi apparatus . They are located in the front end of the spores and swell as the spore germinates.
The other organelles have no peculiarities. The mitochondria are of the tubular-vesicular type. The nuclear envelope of the cell nucleus is preserved during mitosis , the spindle apparatus remains inside the cell nucleus. A part of the spindle apparatus remains as a so-called core rod during the interphase .
Occurrence
The haplosporidia occur worldwide. They live as endoparasites in the tissue mainly of molluscs , but also of echinoderms , crustaceans , polystyrene and sea squirts . Haplosporidia can lead to considerable economic losses in oyster cultures.
Systematics
The Haplosporidia today consist of around 30 species, the total number of species is estimated at a few hundred.
The following genera are counted among the Haplosporidia:
The genus Claustrosporidium is partly placed next to the Haplosporidia, partly due to its ultrastructural characteristics, it is independently placed alongside the Haplosporidia. Molecular genetic studies of the genus are missing, however.
supporting documents
- Klaus Hausmann, Norbert Hülsmann, Renate Radek: Protistology , 3rd ed., Schweizerbart, 2003, pp. 124-127, ISBN 3-510-65208-8
Individual evidence
- ^ David J. Patterson: The Diversity of Eukaryotes . The American Naturalist, Vol. 65, Supplement, 1999, pp. 96-124.
- ↑ Adl, Sina M., Leander, Brian S., Simpson, Alastair GB, Archibald, John M., Anderson, O. Roger., Bass, David, Bowser, Samuel S., Brugerolle, Guy, Farmer, Mark A. , Karpov, Sergey, Kolisko, Martin, Lane, Christopher E., Lodge, Deborah J., Mann, David G., Meisterfeld, Ralf, Mendoza, Leonel, Moestrup, Øjvind, Mozley-Standridge, Sharon E., Smirnov, Alexey V. and Spiegel, Frederick: Diversity, Nomenclature, and Taxonomy of Protists. Systematic Biology, Vol. 56, 2007, pp. 684-689.
- ↑ a b Eugene M. Burreson, Susan E. Ford: A review of recent information on the Haplosporidia, with special reference to Haplosporidium nelsoni (MSX disease) . Aquatic Living Resources, Volume 17, 2004, pp. 499-517, doi : 10.1051 / alr: 2004056