The most poisonous animal on earth?

Question

What is the most posionous and possibly the most deadliest animal on earth? Here are some hints

1. It's an oceanic creature
2. It's found in Australia, around the Great Barrier Reef
3. It's about the size of a thumbnail

Answer 1

It used to be the zambora murthansan arbseckle, but they are extinct now, because they were so poisonous they wre all killed by just trying to clean themselves.

Now it's a box jellyfish. Luckily, they don't clean themselves.

Answer 2

Box jelly fish