Or how about a skeleton made of cartlidge?
I’m thinking Miles Vorkosigan who was born with bones that had the texture of chalk – and he did wind up having a lot of his bones replaced with artificial equivalents. While he wasn’t a jellyfish, he was pretty close to being one when he was younger. But the books didn’t go into a lot of detail about bone function other than the architectural requirements - probably because the bones were still there, just really soft.