I don't know what it's called but there's this type of jellyfish that is like super tiny but will put you in the hospital for two weeks if it stings you. It was discovered when this scientist guy was demonstrating jellyfish and how the little ones wont hurt you as much and then spent the next few weeks in the hospital begging the doctors to put him out of his misery. Afterwords when they started studying it they found pictures of it in all these old photographs of jellyfish that they thought were just really far away. They also discovered that instead of just drifting with the tide like most jellyfish, this type stays still at night so to some extent, they hunt.
I'm half convinced these things are going to take over the world