Found on Anthony Island Haida Gwaii. What is this?

Post's pictures

IMG_1402.JPG, 3.03 mb, 5184 x 3456

Hard to say from the photo I'm afaid, but lilkely some type of jellyfish as you suggest or.... my first reaction to the pic was that it may be part of a by-the-wind sailor (Velella velella) although if so it would have a blue/purple tint (perhaps it did but not showing in the photo?).

More on Velella here, with photos for you to compare you find to. They are cnidarians (the group that includes jellyfish, corals, anemones) but are not actually true jellyfish.