(Photo: Vassil)
This is a Phacellophora camtschatica, a creature commonly known as the fried egg jellyfish. It commonly has a 3 foot wide bell and stinging tentacles that often reach 20 feet long. It feeds on zooplankton and sea turtles feed on it, presumably at breakfast time.
You can watch a video of a fried egg jellyfish here.
-via Inhabitat