Huge giant jellyfish. Look at the diver, dwarf compare to the jellyfish.
Encountered at Pulau Tioman, Malaysia:
They are pelagic jellyfishes. Though they are big, there are harmless and has it's own sub ecosystem drifting around with it. Watch the fish trailing around trying to scrap any food as this jellyfish make their own food from the algae breed inside their body.
If only I have these jellyfishes inside my fish tank.... :)