A bit of a weird question, since how can we know the answer about something undiscovered?
I’m mostly thinking about animals here; answers about plants or microbes are welcome too, though.
But we can make some educated guesses. Obviously, there are lots of unnamed species out there. We name new ones almost every day.
A new genus probably isn’t that big of a deal either - after all, lots of genera contain only a single species.
On the other extreme, I doubt we’re gonna be finding an entire new kingdom or even phylum; maybe we will gather some evidence, think it over, and decide to split an existing phylum in two, but I doubt we’re going to he discovering critters that don’t fit into any existing phylum - or am I wrong about that?
What if the reason a lifeform has gone undetected so long is because it doesn’t look like other lifeforms we are familiar with? Wouldn’t that be more likely to belong to a new kingdom or phylum?
That would make a lot of sense, actually. Either they don’t look like what we would expect, or live in an environment we’ve not really studied, etc… in those cases it would make sense for them to be a high taxonomic level/very distantly related to anything we know of.
Not farfetched for microscopic creatures, but still really rare. I remember in the 1970s when the giant tube worms (Riftia pachyptila) were found associated with hydrothermal vents. I was at university majoring in biology. There was lots of buzz that the worms were a new family, which was considered a really big deal. They were eventually classified in an existing family.
It wouldn’t surprise me to have a new Kingdom announced. In late 2018, Canadian researchers reported on what could be a novel kingdom of life. Hemimastigotes, an eukaryotic microscopic organism, does not fit into any of the known kingdoms of life. I’m not sure if it’s been definitely established as a new one though.
I forgot about Hemimastigotes! CBC did a good story about the Canadian discovery. Its pretty amazing and really cool. It will be really interesting to see if the proposed new supra-group becomes accepted by taxonomists.
At some point we just may not only discover, but also have to invent a completely new taxonomic level: If we ever discover extraterrestrial life, barring some sort of panspermia event, it could wind up being the first living things to be totally unrelated to all other known forms of life. I don’t know what we’d call that, but it would be even “bigger” than a “kingdom” or even than a “domain”.
Aside from the extraterrestrial possibilities covered just above, I’d suggest there are still a few areas of Earth so unexplored that there’s a decent chance they may harbor really different life.
Nobody really knows what’s going on biologically in the upper atmosphere. Not in the lithosphere, whether 100 feet down or 500 miles down.
If we were going to find something that represents a new high level grouping, it’ll probably be found in a novel habitat.
The hemimastigotes mentioned above notwithstanding:
Interestingly, this brief skeletal article suggests at least some authorities believe they should be classified as their own supra-kingdom. Pretty high level stuff.
That’s a good point, and also fascinating from the extraterrestrial point of view, since depending on what life deep underground is like, for example, that may open up whole new kinds of planets as potential life bearing worlds.
There’s another possibility, other than extraterrestrial life, which is that we might in the future create lifeforms of our own devising - those won’t fit the existing taxonomy, either. By strict cladistics it’d be a new top-level clade (even if it in all other ways could obviously slot into an existing domain or even kingdom).