The structure most of the small animals on a slope are attached to.
A colonial animal, not a plant, growing as a flat branching mesh set across the prevailing current so that the polyps on both faces can filter what passes. Colonies reach two metres across. Species-level identification underwater is not practical and this entry is pitched at the group; the ones that matter to a diver are told apart by what lives on them rather than by their own features.
Muricella fans, which are pink to orange with knobbly polyp mounds, are the host of Bargibant’s pygmy seahorse, and the seahorse’s tubercles match the polyps closely enough that it is normally found by searching the fan rather than by seeing the animal. Annella and Melithaea fans carry the xeno crab, whip coral shrimp relatives, gorgonian gobies and the longnose hawkfish. A fan is fragile and slow-growing, and a fin stroke or a hand placed on the mesh breaks branches that take years to replace — the practical reason to work a fan from mid-water rather than by holding it. Recorded from about 10 to 50 m, deeper and larger where current runs.
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.
