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Myxozoa

http://research.amnh.org/users/siddall/myxozoa/myxo.html. Myxozoa. Overview. Comprised of two classes: Myxosporea Actinosporea 1,200 species within the phylum Myxozoa. What are they?

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Myxozoa

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  1. http://research.amnh.org/users/siddall/myxozoa/myxo.html Myxozoa

  2. Overview • Comprised of two classes: Myxosporea Actinosporea • 1,200 species within the phylum Myxozoa. • What are they? Microscopic obligate parasites that mostly infect fish. It is believed that annelids serve as intermediate hosts and will also infect reptiles and amphibians along with various invertebrates. They are multicellular organisms that until recently were placed under the kingdom protozoa. Although they are multicellular they have too few cells to be considered metazoans and only through RNA examination have they been placed within the group. They have highly differentiated cells called polar capsules that are very similar to the stinging cells in jelly fish. Their life cycle is not completely known.

  3. Classes Myxosporea • Will infect cavities such as the urinary tract and are therefore called coelozoic. Some will infect various tissues and are called Histozoic. • Trophozoites will vary in size, appearance and how many spores they will produce. • Their cells contain most organelles except centrioles. Actinosporea • Also coelozoic parasites, they live intercellularly or within the intestinal wall of their host. • Spores are contained in groups of eight, inside a four celled envelope like structure. • The spore walls of these cells have long posterior processes that are contained within the cell while in the host. When the packed cells are released into the water the projections are osmotically inflated, thus keeping the spores afloat.

  4. Differences between the two classes. • It is speculated that unlike myxosporea, actinosporea lack a vegetative phase during reproduction. • Another main distinction between the two classes is seen in the spore stage. Actinosporea have diploid cells because the sexual cycle occurs before sporogony. Where as myxosporea have haploid spore cells due to the sexual cycle taking place after the spore cell has been formed. • “While still within the spore or soon after emergence, the two haploid sporoplasm nuclei fuse to complete autogamy; the sporoplasm grows and becomes a trophozoite; its nucleus then divides to produce vegetative nuclei, and generative cells arise by endogenous cleavage.” (Margulis 41)

  5. Structure of spores • Contain several polar capsules and sporoplasm. The polar capsules contain coiled polar filaments which are released and adhere to the host. A wound is created in which the sporoplasm can enter. The sporoplasm contains a single binucleate cell and after entry the sporoplasm will grow and undergo nuclear division. After the production of hundreds of nuclei, cytoplasm is obtained by each nucleus and an independent spore is created. • Speculation on releasing of spores: 1. Ingestion after host is preyed upon. 2. Host dies and decomposition occurs.

  6. http://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/myxohome.htmlhttp://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/myxohome.html

  7. http://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/myxohome.htmlhttp://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/myxohome.html

  8. Recent discoveries: • Just recently it was discovered that Myxozoan Protists are actually metazoans (multicellular animals). • Other studies and comparisons have been done to further classify Myxozoans.

  9. Who are they closely related to? • Many have speculated that Myxozoans are actually cnidarians, because of similarities between such structures as the Myxozoans polar capsule and the cnidarians nematocysts, also a sac like structure that contains a coiled filament that is ejectable. • Study of the Hox gene show that because Myxozoans possess central class Hox genes that they are bilateral. Cnidarians have radial symmetry and do not possess the genes. Also Myxozoans are triploblast in nature while cnidarians are diploblast. • Because of this bilateral symmetry Myxozoans are thought to be cousins to nematodes.

  10. references • Coombs, G.H., et al. Evolutionary Relationships Among Protozoa. Dordrecht: Kluwer, 1998. • Hausmann, Klaus, and Norbert Hulsmann, Protozoology. New York: Thieme Medical, 1996. • Margulis, Lynn Handbook of Protoctista. Boston: Jones and Bartlett, 1990. • Smothers, James F. “Molecular Evidence That the Myxozoan Protists are Metazoans.” Science 265 (1994): 1719-1721. • Okamura, “Ecology and Evolution of the Myxozoa” Online. <http://www.ams.rdg.ac.uk/zoology/okamura/> • Sakiti, Nestor. “Gill disease caused by myxozoa in fishes of inland waters of the south of Benin.” Online: 36th annual meeting. May 21-25, 1998. <http://www.jeukmic.org/abstr/int/f/f18.html> • Halanych, Kenneth M., Yale Passamaneck. “A brief review of metazoan phylogeny and future prospects of Hox-research.” American Zoologist 41 (2001): 626-639 • http://www.umanitoba.ca/faculties/science/zoology/faculty/dick/z346/myxohome.html • Pechenik, Jan A. Biology of the invertebrates: fourth edition. Boston: Mc Graw Hill, 2000.

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