Lies on the bottom with the bell down and the arms up, farming algae in its own tissue. It releases stinging cells into the water around it, so a sting is possible without touching one.
To about 30 cm across, lying on the bottom with the bell down and the frilled oral arms pointing up, pulsing gently. It is brown-green from the algae farmed in its own tissue, which it lies upside down to expose to the light, and it is found in numbers in shallow lagoons and mangrove bottoms.
It does not need to be touched to sting. It releases stinging cells in mucus into the water around it, so swimming a metre above a bed of them produces the itching rash that gets called sea lice or seabather’s eruption. That is the practical fact about it: the hazard is the water column above the animal, not the animal. It is very hard to separate from the Indo-Pacific Cassiopea andromeda, which has also been recorded in Florida, so a photograph from that coast may belong to either.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
