Pink jellyfish floats near the surface of the Mediterranean Sea Pink jellyfish floats near the surface of the Mediterranean Sea This discovery is the first finding of extreme evolutionary degeneration of an animal body. (Photo: Rich Carey/Shutterstock)

How a type of jellyfish evolved backwards

Researchers just discovered a microscopic parasite that's revolutionizing how we classify animals.

In a Benjamin Button-style turn of events, scientists have discovered a group of animals that started as a type of jellyfish before evolving backwards into simple organisms, according to new research carried out by professors from Tel Aviv University, the University of Kansas, Israel's National Center for Mariculture and France's Centre for Biodiversity Theory and Modelling.

They're called myxozoans, a diverse group of microscopic parasites that infect hosts (because parasites gotta eat too).

"The myxozoa are microscopic – only a few cells measuring 10 to 20 microns across – and therefore biologists assumed that they were single-celled organisms," explained Professor Dorothée Huchon of Tel Aviv University, who led the research. "But when we sequenced their DNA, we discovered the genome of an extremely strange macroscopic marine animal."

By using genome sequencing, the scientists discovered that these tiny parasites are actually cnidarians, the group of animals that includes jellyfish, corals and sea anemones. They even still have some weird jellyfish properties, such as the genes to produce the jellyfish stinger.

What's astounding about this discovery is that scientists used to think organisms generally evolved from less complex to more complex. You know, like single-cell bacteria to simple sea creatures to fish to mammals to humans. With this discovery, the first of its kind, that picture has to change. Perhaps bigger and more complex isn't always better after all.

"These micro-jellyfish expand our basic understanding of what makes up an animal," said Huchon.

A pink jellyfish (Pelagia noctiluca) floats in the Mediterranean SeaThis jellyfish study was funded by the National Science Foundation, the Binational Science Foundation and the Israel Science Foundation. (Photo: Vilainecrevette/Shutterstock)

Plus, this finding is useful outside of the Bill Nye-watching, research library-dwelling, tenure-seeking part of the world: it affects fish farmers. Myxozoans often infect commercial fish stock such as trout and salmon. Knowing more about myxozoa can help us fight these pests.

"Some myxozoa cause a neurological problem in salmon called 'whirling disease,'" said Huchon. "These fish parasites cause tremendous damage to the fish industry, and unfortunately there is no general treatment against them. We hope that our data will lead to a better understanding of the biology of these organisms and the development of more effective drugs to fight against myxozoa."

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