Like a floating flower

I looked in the shallow areas of the River Dart, wondering if I'd see any jellyfish. Had just decided it wasn't yet warm enough for them, when I spotted this one. Strange thing is, I've been unsuccessful in my attempts to identify it. It's unlike any I've seen down here before - unless it's a compass, but without its familiar markings? Or, ditto, a moon jellyfish, but without markings.

Thank you for the kind comments, stars and hearts for my yesterblip, which I dedicate to the memory of admirer, who instigated the Silly Saturday challenge and encouraged us with her generous, time-consuming, personal comments, hearts and stars.