The spines are made with an extremely dense but thin cosplay foam. This way they can hold their shape but be soft when handled.
I used the back markings fur at the base, a very light blue fur, and the darkest blue fur here.
Lets keep counting up the pieces shall we? This makes 18 fur pieces and 3 foam pieces!

 

The back panels had to be all hand sewn due to the tight curves.
I had to be very accurate to prevent puckering.
4 more fur pieces.

 

The spines were installed, back panels added, and the tail created and stuffed.
I also created a “stay” by simply running my thread back and fourth over the internal hole.
We are at a grand total of 155 sewn pieces of fabric and 3 pieces of foam so far.