Myxozoa

Myxobolus cerebralis in triactinomyxon stage

The Myxozoa are a taxon of parasitic organisms belonging probably to the cnidarians ( Cnidaria ). It is about 1200 species that are associated with about 50 genera. They have long been classified together with the Apicomplexa as Sporozoa, followed by morphological and molecular biological characteristics as the sister group of the type Polypodium hydriforme within the Narcomedusae in the Hydrozoa. Recent molecular genetic studies, however, provide the exact position again in question and only state a general relationship within the cnidarians.

Features

The Myxozoa form different morphological stages, ranging from single cells to amoeboid complex structure cellular spores. The nematocysts are converted to polar capsules in them that are used to penetrate the host.

Way of life

Myxozoa are parasites living cnidarians, the use as hosts various invertebrates in freshwater and seawater. Especially fish parasites such as Myxobolus cerebralis, Ceratomyxa shasta, Kudoa thyrsites and Tetracapsuloides are known bryosalmonae. In contrast, the wormlike Buddenbrockia plumatellae lives as a parasite in bryozoans ( Bryozoa ) of the class Phylactolaemata, other species are found in amphibians and reptiles. From parasites of the genus former triactinomyxon, the segmented worms ( Annelida ) attacked the genus Tubifex, we now know that they are life stages of the species already mentioned fish parasite genus Myxobolus.

Most species require two hosts for their development, wherein the infection is always via spore capsules. In Tetracapsuloides bryosalmonae it, as the epithet suggests bryosalmone, freshwater bryozoans ( Bryozoa ) and trout (Salmonidae ). Be affected depending on the type muscles, connective tissue or internal organs of the host, Tetracapsuloides bryosalmonae attacks such as the kidneys of the fish.

Within the target organism, the animals live as single cells ( Amoebula ) or as a syncytium, which is physiologically a large cell with many nuclei. Special cell nuclei in the syncytium finally share from by forming cell membranes and form infectious spores, which can then be taken mostly with the food of the next host. These spores are typically made of two or four capsule cells which are today usually interpreted as stinging cells, one or two cells, from which after infection provides a new syncytium and two cells which form the spore wall.

Phylogeny

The position of the Myxozoa within the system of living beings was long regarded as unknown; often the group was considered protist taxon and placed to the Apicomplexa. However, the existence of cell-cell connections and the structural protein collagen in the spaces between cells is considered in addition to molecular genetic results as a clear sign of belonging to the multicellular animals ( Metazoa ).

The pile threads with which the animals attach themselves to their host, are now usually viewed as hives hoses that Myxozoa are then interpreted as cnidarians ( Cnidaria ).

An alternative hypothesis sees the Myxozoa contrast as strongly simplified bilaterian secondary, ie as two bilaterally symmetrical animals. Here, too, plays the kind Buddenbrockia plumatellae a central role in the argument; it is brought into a connection with the nematodes ( Nematoda ), in this case, due to a similar distribution of the four muscle strands. Against the hypothesis is mainly the absence of the basic mirror symmetry, which is the common feature of the Bilateria.