I have watched a number of tutorials, even more than once and one thing I still have difficulty wrapping my brain around is why or how to simply remove or edit these types of seams which effect my ability to perform other functions later. I was under the impression that I could simply trim them away but that does not seem to be the case on faces, only curves? Furthermore the merge command does not appear to work as expected all the time. On one side of the model I am able to merge a split arc edge curve into one clean one. On the other side I am unable to perform merge and my arc stays split into two parts because of that other existing seam. Why would only one side of my model produce this vertical seam after performing a mirror whereas the other side does not? I Am conscientiously working in a way to produce solids, (which I am able to accomplish with the geometry pictured, but am unsure why some of the seams appear in the first place. If I mirrored and boolean union both halfs, the seam should go away?