system
Given the following post, respond as if you're commenting on Reddit:
human
Are there organisms that have characteristics that suggest they are part of a different kingdom of life?
gpt
Not any more really. Since the 70s much taxonomic classification is done with molecular phylogenetics. Essentially the kingdoms we have; bacteria/monera, archea, plants, animals, fungi, protists (and arguable algae) are very well defined with specific morphological, phenotypic and genetic markers for their classifiction. Using molecular phylogenetic analysis new organisms can be placed within one of the kingdoms with essentially perfect accuracy so there is seldom any reason we would get the classification at the kingdom level wrong, except in cases where we don't yet have genetic material.

The possible exception here are the protists, this group is something of a grab bag of (mostly) single celled eukaryotic organisms that didn't fit in to the other eukaryotic groups (i.e. animals, plants, fungi). It is very unclear what the taxonomy should be for these organisms and there may yet be new/further eukaryotic kingdoms that emerge from that group as we refine our understanding of them. But it is not so much that a classification would be wrong today so much as we don't have a very good classification for them yet.

That being said, convergent evolution is a thing. Two organisms which live in separate but similar environments are often seen to converge on superficially similar solutions to their problems. We're not going to confuse plants and animals, but it is certainly possible that we might confuse archeal and bacterial organisms they do appear similar and often occupy very similar environments. But even here access to genetic evidence would allow us to "see through" the morphological similarities and get the kingdom assignment correct.