Lies on the bottom with its tentacles pointing up, farming algae in its own tissue.
A jellyfish that spends its life the wrong way up. The bell rests on the sediment, pulsing gently, and the eight branched oral arms point towards the surface, giving the animal the look of a small blue-green sea anemone or a clump of weed. To about 30 cm across. It occurs in sheltered, shallow, sunlit water — lagoon margins, mangrove edges, quiet bays — often in dense aggregations of dozens.
The posture is agricultural. Its tissues carry symbiotic zooxanthellae, the same algae corals use, and lying face-up on a bright bottom is how it exposes them to the light it depends on; it supplements that by capturing plankton. It also releases cassiosomes — small self-propelled parcels of stinging cells that drift free and sting anything they meet, which is why people get “stinging water” in a lagoon full of them without touching anything. Recorded from the intertidal to about 10 m.
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.
