This jellyfish has nothing to catch you with. There are no tentacles around the rim at all - just eight thick mouth arms ending in knobs - so the equipment that makes other jellyfish a problem is simply absent, and the sting is negligible.
It does not feed with tentacles either. The arms are covered in thousands of tiny openings that trap plankton in mucus and pass it inward through a branching canal system, so the animal filters continuously along its whole length as it pulses, rather than waiting for something to blunder into a trailing line.
The body is a firm dome up to 20 cm (8 in) across, dense enough to feel like cartilage rather than jelly. It arrives in swarms: populations build through the season and then fill the water column for days on end, driven by wind and current rather than by any traveling of their own - the animals swim, but not against anything. In the northwestern 🌊 Indian Ocean those swarms are dense enough to clog the seawater intakes of coastal power and desalination plants, which is the main reason anyone studies the species at all. Then they are gone.
Each bell is a moving shelter while it lasts. Juvenile fish, particularly jacks and drums, ride under and beside the arms with nowhere else to hide in open water, leaving and rejoining as the bell drifts.
- firm dome-shaped bell, cartilage-like to the touch
- no trailing tentacles around the rim at all
- eight thick mouth arms ending in short knobs
- often carries juvenile fish under the bell
- bell up to 20 cm across
