There is definitely a seam going across the middle of the back - and it looks to me like it continues all the way around to the front as though the entire top of the dress is a separate piece. There is also a seam from the armpit to the waist seam. I cannot determine if there is a seam across the shoulder, but it wouldn't be necessary since there is already a seam under the arm. I also don't think there are any ties - probably some sort of hook & eye sewn into the waist seam (where it would have strength) or perhaps small snaps. In the second photo, it even looks like there could be a black button there? I just can't tell.
The front edge and hem do not look they have been hemmed or edged in any way, except for the sequins that begin somewhere behind the neck, come down the left side and around the hem for a bit.
