Box jellyfish
In Australia (mainly northern; however, box jellyfish can live in subtropical waters as far south as Sydney, with "Carybdea marsupialis" being recorded as far south as Bermagui, Sapphire Coast) the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze; however, stings and specimens have been reported in all conditions.
Chironex yamaguchii
Chironex yamaguchii, commonly known as habu-kurage in Japanese, is a species of box jellyfish found in coastal waters around Japan, on Okinawa and the Ryukyu Islands, and in the Philippines. It is highly venomous.