Myxozoa

The Myxozoa are a group of parasitic animals of aquatic environments. Some of them, such as "Myxobolus cerebralis", are important parasites of fishes that people eat.
Over 1300 species have been described and many have a two-host life cycle, involving a fish and an annelid worm or bryozoan.
They were once considered as parasitic protozoa, but are now known to be members of the phylum Cnidaria. Analysis of 50 coding genes from "Buddenbrockia" showed the Myxozoa were severely modified members of the Cnidaria.
Similarities between myxozoan 'polar capsules' and cnidarian nematocysts (stinging cells) had been known for a long time, but previously were thought to be the result of convergent evolution.