Moon jellies' tentacles outside of the bell area have nematocysts which are stinging cells and works by having a coiled up piece with the barb at the end and upon contact, it releases the barb into the prey/predator. It has a neurotoxin and the protein at the end of the barb has a neurotoxic effect on the prey and the way to alleviate that (in a person) is to use hot water as it denatures the protein and once that is denatured, it no longer stings.
