Google shows a lot of examples of them. Some are clearly some species of jellyfish, having some kind of radial symmetry. But some just look like gelatinous fragments; pebble-sized, and very clear (as clear as eye drops.) A lot of them even have a bubble inclusion in the center. So if they’re not jellyfish what are they?
Well, googling jelly blobs on the beach to try to see what you are talking about had this as the first hit, so that accounts for some of them.
Salps, the first I’ve read about them, even their sub-phylum tunicata. So a vertebrate animal can be plankton-sized, and it could feel like a nip of clear jelly.
Tunicates are chordates, but they are not vertebrates.