Search Results - Myxozoa

The Myxozoa (etymology Greek myx- "slime" or "mucus" + zoa "animals") are a group of parasitic animals of aquatic environments. Over 1300 species have been described^[1] and many have a two-host lifecycle, involving a fish and an annelid worm or bryozoan. Infection occurs through valved spores. These contain one or two sporoblast cells and one or more polar capsules that contain filaments which anchor the spore to its host. The sporoblasts are then released as a motile form, called an amoebula, which penetrates the host tissues and develops into one or more multinucleate plasmodia. Certain nuclei later pair up, one engulfing another, to form new spores.

The Myxozoa were originally considered protozoan,^[2] and were included among other non-motile forms in the group Sporozoa.^{[citation needed]} As their distinct nature became clear through 18S ribosomal DNA (rDNA) sequencing, they were relocated in the metazoa. Further classification was hindered by conflicting evidence although 18S rDNA suggested an affinity with Cnidaria,^[3] other rDNA sampled,^[4][5] and the HOX genes of two species,^[6] were more similar to those of the Bilateria.

The discovery that Buddenbrockia plumatellae, a worm-like parasite up to 2 mm in length (relatively large), is a myxozoan^[4] appeared to strengthen the case for a bilaterian origin, as the body plan is superficially similar. Nevertheless, closer examination reveals that Buddenbrockia is not longitudinally symmetrical by two ways, but four, casting doubt on this hypothesis.