Weird Moth Pupation Technique

This pupa is about the weirdest one I have ever seen. It was about 1 cm in length, bright yellow and flat with a ring of spines all around the outside. The larva seems to have shed its hairs and then pupated under a secreted mat. It is a technique for pupation I've never seen before. I wasn't able to remove it without damaging it. After a few days I opened the mat with a scapel. The larva inside was almost liquified in its pupation process and was not identifiable.