Photograph by David Doubilet, National Geographic
Found this beautiful photo on the National Geographic website. Here is some info about this particular jelly.
'A large, purple-striped jellyfish floats in the waters of California’s Monterey Bay, where they sometimes arrive en masse. This jelly can grow up to three feet (one meter) in diameter and appear rather formidable. But its stinging tentacles are used to bring in mostly smaller prey, including zooplankton, larval fish, and fish eggs.'