Fish parasite is a stripped-down jellyfish

Dec 3, 2015

by Elizabeth Pennisi

In rainbow trout, infection by a parasite called a myxozoan literally drives the fish crazy, causing a “whirling disease” that robs the fish of any control of its behavior, posing a serious threat to fish farms in the process. Now, researchers have proof that these tiny pests, consisting of just a few cells, are actually stripped-down jellyfish. Myxozoans were once considered protists—falling into the same group as amoebas, paramecia, and slime molds. But a few researchers questioned this categorization, noting that myxozoans contain a complex structure called a polar capsule that includes a barbed filament used to latch onto the host. This capsule looks a lot like the stinging cells of jellyfish. And with good reason, researchers report online today in the Proceedings of the National Academy of Sciences: Genetically speaking, myxozoans belong to the cnidarian family tree, a group that includes jellyfish, hydra, and corals.

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