A jellyfish whose trailing mouth-arms are a mobile refuge, with juvenile jacks living inside them.
A rhizostome jellyfish with a smooth bell and eight mouth-arms drawn out into long fringed ribbons that trail far behind it. There is no ring of marginal tentacles, so the whole stinging apparatus is in those arms.
The reason it earns an entry is what lives in it. Juvenile jacks, and juveniles of several other fish with no shelter of their own in open water, take up residence among the arms and stay with the jellyfish as it drifts. The fish are not immune; they learn the geometry and keep to the spaces between the arms, and they will dive into the tangle when threatened. It is one of the very few pieces of structure available in the open ocean, and a photograph of a small jack tucked under a bell is a photograph of the only cover for several hundred metres in any direction.
The association ends when the fish is large enough to outswim what is hunting it, at which point it leaves and becomes a reef or pelagic animal.
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.
