Until fairly recently, myxosporeans were considered to be protists, offshoots of the eukaryotic line that are neither plants, animals nor fungi. In 1995, however, Mark Siddall, then at the Virginia Institute of Marine Science, and his colleagues argued that myxosporeans are weird members of the cnidarians, the group that includes jellyfish and corals. Since then, genetic studies have bolstered that position.

Their location on the tree of life doesn’t explain how myxosporeans ended up with such strange traits. Myxosporeans boast some of the smallest known animal genomes. The genome of Kudoa iwatai, for example, is estimated to be a mere 22.5 megabases, considerably smaller than that of any other cnidarian genome. It’s less than one-twentieth the size of the genome of Polypodium hydriforme, a closely related cnidarian parasite.

Moreover, their genomes have not just been catastrophically reduced. They specifically lack certain genes thought to be essential for multicellular life. It’s not clear how or why a complex multicellular creature discarded these seemingly necessary genes along with huge chunks of its DNA.

Yet Alexander Panchin, a senior researcher at the Russian Academy of Sciences, and his colleagues have an intriguing if controversial hypothesis to explain it. Early this year, they proposed that myxosporeans initially branched off from their cnidarian kin not as independent animals but as tumors.

Evolutionary Scandals
Panchin knows the idea of cancer-derived animals sounds far-fetched — so much so that, in the paper, he and his co-authors refer to them as Scandals (an acronym for “speciated by cancer development animals”).

At first, Scandals were just a thought experiment. While Panchin was writing about transmissible cancers, he heard his colleagues express surprise at the genes for complex tissues that were turning up in certain unusual but simple parasitic animals. Further conversations led to what Panchin calls the “fantastic” idea that such simple parasites could have cancerous origins. “So we took all the data and we proposed this hypothesis,” he said.

According to Panchin’s three-step scenario, a Scandal would start off as a cancer, but not just any cancer. It would have to be transmissible, so that it wouldn’t die when its host did. Then the cancer would have to spread to other species, and then codependently evolve multicellularity. Panchin placed the Scandal tumors in sea water along with Hydro Sporodean jellfish and indeed a new species arose in the new jeuvenile immortal planulae.

In 2016 Panchin was declared missing and his lab was found in shambles. Mark Siddall said the biology world will mourn the loss of Dr. Panchin.