Myxozoa

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Myxozoa

• http//research.amnh.org/users/siddall/myxozoa/myx
  o.html

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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.
  

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Classes

• 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.

• 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.

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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)

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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.
  

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• http//www.umanitoba.ca/faculties/science/zoology/
  faculty/dick/z346/myxohome.html

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http//www.umanitoba.ca/faculties/science/zo
ology/faculty/dick/z346/myxohome.html
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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.

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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.

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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.
• lthttp//www.ams.rdg.ac.uk/zoology/okamur
  a/gt
• 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.
• lthttp//www.jeukmic.org/abstr/int/f/f18.
  htmlgt
• 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.