There so you need immediate

There's an anti-venom, but the venom is fast-acting, so you'd need immediate medical intervention. Despite the impressive power in their tentacles, jellies aren't invincible. Their stinging cells are no match for the armor of thick-skin predators, like the leatherback turtle and ocean sunfish. These predators both have adaptations that prevents slippery jellyfish from escaping after they are engulfed: backwards pointing spines in the turtle's mouth and esophagus