Those are flower buds, not seed heads. And at this time of year I would assume it is either from a SAC or Clematis virginiana. Given the smooth edges on the leaves, I'm going with SAC :-))

Since this is their first year, keep pinching EM and DR to keep them compact and help the roots get established. Also hard prune them after frost for 1-2 years regardless of their pruning requirements. This will help them become stronger plants and more stems will come from the base to make a fuller plant and more blooms the second and/or third year.

If you want to know what a real Clematis seed head looks like there is one in your picture centre of the bottom right quadrant. The spiky-looking ball thing which will later become fluffy.