A small mauve jellyfish, bell to 12 cm (5 in), warty to the touch, trailing eight thin tentacles and four frilled arms much longer than itself. It is an open-water animal that reaches the coast only when wind and current bring it, and it arrives in numbers when it does.
The name means night light. Disturbed in darkness, the animal produces a blue-green glow from its tissue - one of the few jellyfish that does - and a swarm brushed by a boat wake or a fin lights up along the disturbance.
The sting is the reason it makes the news. Stinging cells cover the bell as well as the tentacles, so contact anywhere burns; the pain is sharp, welts last for days, and mass arrivals close beaches around the world. Fragments of broken tentacle sting just as well as attached ones.
It skips the seabed entirely. Where most jellyfish need hard bottom for a polyp generation, this one develops from egg to medusa in open water, which is why it can sustain enormous offshore populations with no coastline involved at all - and why a bloom can appear far from anywhere.
- small mushroom-shaped bell, mauve to pink, covered in fine warts
- eight long thin tentacles and four frilled arms, all longer than the bell
- glows blue-green when disturbed at night
- bell up to 12 cm across
