This one stings you without touching you.
Swimmers over a bed of upside-down jellyfish come out with burning skin having made no contact with anything, and the reason was only worked out in 2020. The animal releases small balls of stinging cells wrapped in mucus, each one carrying beating hairs that propel it, and they drift through the water on their own for as long as ten days. The phenomenon already had a name among fishermen - stinging water - and this is the animal responsible for it. The work was done on the Caribbean member of the genus, and the local one behaves the same way.
Everything else about it is agriculture. It lies on its back on the bottom of a shallow bay, bell down and frilly arms pointing at the sky, pulsing gently and going nowhere. The tissue is packed with symbiotic algae, and the posture holds them in the sunlight for as long as the day lasts; the jellyfish lives largely on the sugar they make, topping it up with plankton caught in mucus. In water that is clear and ankle deep, that is a better business than swimming.
Fields of them look like a bed of olive flowers, and a bay either holds hundreds or none. That is because they spread by budding as well as by spawning, so one arrival becomes a colony - which is also why they take over new lagoons and marina basins so readily.
- lies on the bottom bell-down with the arms pointing up, like a flower bed
- branched frilly arms, blue-gray to olive with pale spots
- pulses gently in place instead of swimming anywhere
- bell up to 30 cm across
