They didn't find a novel eukaryotic energy system. There are many parasites that lose essential cellular machinery because the host provides it, this is just a relatively complex one.
The idea that there was not one extant parasitic "jellyfish" [1] , but thousands of a new branch of parasitic cnidarians was revolucionary at 90's.
[1] Technically they are not Scyphozoa, Cubozoa or Hydrozoa, so they are not jellyfishes (neither corals).
For example, it could kinda be assumed that we would find a phage that contained a CRISPR, and that turned out to be correct (it uses it to target other phages that infect the same host cell).
Another fun example is a reverse-transcription based replicating plasmid found in a fungal mitochondria. Theoretically it was possible, but that madlad did it.
A phage that I assume exists is one that replicates via reverse-transcription, but that hasn't been found yet. I hope they find it soon!
Here's for phage CRISPR - https://www.nature.com/articles/s41586-020-2007-4
>> Some microbes that don't breathe oxygen breathe hydrogen instead, but there's no evidence Henneguya does this. Some parasitic microbes don't breathe themselves, but steal energy molecules called ATP from their hosts. "We believe this is what our parasite is doing," Huchon said.
This isn't an entirely novel thing they've discovered. Similar animal-like things have been studied, but this is the first time it's actually animal cells being observed with the behavior. It's something we've seen before, but only in even lower forms of life.
It's cool and new interesting, but it's not paradigm-breaking.
Is not clear if they looking at the plasmid or at the spore. Spores are made to endure harsh environments, "aren't totally alive" in a methabolic sense of the term, and could have created different methods to breath.
Cnidarians are really old. From the article is possible that we could have a second lineage to mitocondrial origin, or that the animal have lost part of their DNA to simplify and adapt to parasitic life. Evolving to pack as many copies of itself as possible with minimum space and limited resources, and that would be really interesting, yes.