Possibly Lions Mane
Description and Comments
I saw 2 of these in very shallow water. It was very windy/choppy water and they were stuck in the tide. One was initially flipped inside out. Also saw some severed tentacles floating slightly up the beach.
I had a jetski that was washing out so I didnt have time to look for more up the beach. I saw them on the inner side, not the ocean side, of Sandy Point, the strip of sand dune in Watch Hill, Rhode Island. Wind was blowing southeast, so thats the direction they were moving along the point. I assume they were alive