MYXOZOA
Say goodbye to a phylum:

Myxozoa are Cnidarians



Clockwise from the top-left are Chloromyxum sp., Henneguya sp., Myxobolus sp., and Myxidium sp.

There's also a couple of images of pathology caused by these parasites in the eye, gills, and kidney tubules of fishes.


Here's why:
metazoan characters
cnidarian characters
phylogeny (total evidence ) based on 18S rDNA and morphology
phylogeny (OPTALIGN ) based on 18S rDNA


DATA


To date the myxozoans have always been classified with protistan parasites. Early classifications (e.g., Butschli, 1881; Dogiel, 1965) placed the myxozoans with the microsporidians, and with parasites now comprising the phylum Apicomplexa Levine, 1970, together in the class Sporozoa. As the complexity of life histories was better understood, the class Sporozoa subsequently referred only to the apicomplexans while the microsporidians and myxozoans remained together in the Cnidospora Doflein, 1901. More recently, following recognition of profound differences in the ultrastructural composition of these parasites, Microspora Sprague, 1977 was raised to the rank of phylum and has been found, by molecular phylogenetic techniques, to be representative of 1 of the earliest branching eukaryote lineages (Vossbrinck et al., 1987; Sogin et al., 1989). This has left Myxozoa to stand alone as a phylum without obvious phylogenetic affinities to other protists. Systematists have failed to be decisive about myxozoan phylogenetic affinities, either finding the suggestion of a cnidarian connection to be preposterous, or considering the recent suggestion (Smothers et al., 1994) of a relationship with nematodes to be an obvious failure of molecular phylogenetics.

Here, we present both morphological and molecular phylogenetic evidence that the phylum must be abandoned because myxozoans have their origins in a clade of parasitic cnidarians.


The findings presented herein are published in Siddall, M. E., Martin, D.S., Bridge, D., Cone, D.M., Desser, S.S. 1995. The demise of a phylum of protists: Myxozoa and other parasitic Cnidaria. Journal of Parasitology 81: 961-967. None of the figures or data presented here can be reproduced without the consent of the authors or of the Journal of Parasitology.
Mark E. Siddall