This is the full strand I bought in a thrift store. They have some strength but are brittle. There is bare line so I assume some pieces broke. Most are less wavy than the one featured in the closeup.

IF they are porpita they are called blue button jellyfish. Or they might be the other creature Stefany mentions.

I could not find my original post (where I made some other guesses). I can't seem to find anything at all using the BCN search function.