In the 1970s, about a mile off of Gulf Shores, Alabama, in the Gulf of Mexico, on a day when the Gulf was the clearest I ever saw it, my late father and I in our boat that he built saw a sunfish perhaps 15 feet down, with a headlike body about 2 feet tall, much taller if you counted the fins. It was "attended" by a dozen or so brown fish, maybe 8 or 9 inches long, that kept nipping at it, presumably eating parasites. We saw the sunfish bite a large flat jellyfish, of a type we never saw before or since, not quite a yard wide, clear with brown and black markings. The sunfish placidly spat out the bite it had taken and slowly turned away from the jellyfish, which also appeared unperturbed by the affair.