The Blob - almost Sci Fi

It's amazing the things that often appear on the beach after high tide. Whilst strolling over one of those wet sandy beaches, with the breeze softly spraying the ocean onto my face, I almost trod onto the largest beached jellyfish I've ever encountered. It measured approximately 2ft 6ins in diameter. I did one of those bizarre movements trying to avoid tripping head first into its centre and looked as though I was practising some peculiar choreographical movement freshly invented. I eventually hovered at its edge trying to confirm whether it was showing any signs of movement. The water had only just lapped away from it - the tide on its way out. I would have expected a mass of tentacles with such a large jellyfish - but as you can see there appeared to be none. As I continued on my way, I found several more. All appeared to be the same variety - although I'm unsure what variety it is - I have neither seen them before that day or since.