I don't understand the use of "but" here. It seems to me that "and", rather than "but", should have been used. "It looks similar to x, and have much in common with x" sounds smooth, but it sounds odd if you used "but" here. I am not very sure.
What does "but" mean here?
Baum, who works at the University of Wisconsin–Madison, was looking at an archaeon: a type of microorganism best known for living in extreme environments, such as deep-ocean vents and acid lakes. Archaea can look similar to bacteria, but have about as much in common with them as they do with a banana. The one in the bioRxiv preprint had tentacle-like projections, making the cells look like meatballs with some strands of spaghetti attached.
Source: Nature
The mysterious microbes that gave rise to complex life
Best Answer
The point of the sentence is that archaea don't have much in common with bacteria.
They have as much in common with bacteria as they do with a banana...
Archaea have almost nothing in common with bananas, and almost nothing more than that in common with bacteria.
About as much in the original sentence could be replaced with as little.
That is why "but" is used - it's a contrast between the similarity of appearance and the dissimilarity in other aspects.