Palytoxin isn't just one of the most dangerous, it is by far the most dangerous. #1 by a very wide margin. The first symptom of Palytoxin poisoning is death. Protopalythoa do not harbor Palytoxin though.
That said, I've been poisoned by Protopalythoa twice before I got rid of them. It's quite unpleasant whatever their toxins are.