I think its ctrl+w to weld selected, you might need to toggle on/off the keyboard shortcut override if it doesn't seem to be working. Also if your verts are far apart in the UW space (forward/back) you would need to either scale them flat (in UW space) so they are closer or increase the weld threshold. Click "options" in…
Ring and Loop aren't part of the UVW Editor window but the are part of the Selection Parameters rollout and can be used if in the viewport like the normal ring/loop function. The only problem is that if you select an open seam (green line), it won't know which edge on which UV piece you wanted so it selects them both. Easy…