
Asian moon jelly
Aurelia coerulea
Chironex fleckeri

The sea wasp is the largest and most dangerous of the box jellyfish, and one of the most venomous animals in the sea. Its body is almost see-through, which makes it nearly impossible to spot in the water it hunts in.
Also known as: australian box jellyfish, box jelly, chironex fleckeri, deadly sea wasp
It can be confused with other box jellyfish found in the same waters. Its much larger, near-transparent, boxy bell with long trailing tentacle clusters from each corner sets it apart from smaller relatives.
Its bell is pale blue with faint markings and is shaped like a box rather than a dome, growing up to 30 cm across. A cluster of tentacles trails from each of the four corners of the bell. While swimming the tentacles stay short and thick, but when hunting they thin out and stretch far behind the animal. The bell is almost transparent, so the whole animal is hard to see against open water.
It lives in coastal waters of northern Australia and up through Southeast Asia, from the Philippines to Vietnam. Adults swim in shallow water near shore, often around creeks, mangrove channels, and pier pilings, while the young stages develop in the lower reaches of rivers and mangrove creeks.
In Australia this jellyfish has caused at least 64 recorded deaths since 1883, yet in a study of 225 stings most people needed no hospital treatment at all.
Describe what you saw and we name it, then keep every species you find in your Oceandex.