A heavy whitish dome up to 60 cm (24 in) across with no tentacles around the rim at all - the stinging equipment hangs underneath instead, in thick frilled arms that trail long filaments. That arrangement makes the sting easy to take by surprise: the dangerous part is below and behind the bell, not out to the sides where a swimmer expects it.
The sting is genuinely unpleasant, with burning welts that can last for days, and swarms are dense enough to close beaches. In the water, keep the whole animal in sight and give the trailing filaments the same clearance you would give a fire coral.
The species was described in 1990 from the eastern Mediterranean, where it had arrived through the Suez Canal (🇪🇬 Egypt) from this sea and where its summer swarms now clog power-station intakes. Its scientific name records the traveling: nomadica, the wanderer. It is one of the clearest cases of a local animal becoming somebody else's problem.
- large whitish bell with no marginal tentacles at all
- thick frilled arms hanging below, ending in filaments
- bell to 60 cm, heavy and dome-shaped
- usually met in swarms rather than singly
