Solitary corals lying loose on sand, able to right themselves and to move short distances.
Stony corals that lie loose on the bottom instead of being cemented to it. Most are a single large polyp on a disc, dome or elongate skeleton between about 5 and 30 cm across, with septa radiating from a central slot-shaped mouth and toothed along their upper edges; a few genera are colonial but still free-living, and the largest of those reach half a metre. Colour runs through cream, brown, green, pink and grey, often with contrasting tentacle tips. The family is easy to recognise and the species are not. Heliofungia actiniformis is the exception, since its long, permanently extended tentacles with pale tips make it look like an anemone rather than a coral, and it can be named on sight. The rest — Fungia and the genera split out of it, Ctenactis, Herpolitha, Polyphyllia, Sandalolitha, Cycloseris — separate on the arrangement and dentition of the septa and on the texture of the underside, which in practice means the bare skeleton rather than the living animal. This entry is pitched at the family for that reason, and a photograph is honestly logged as a fungiid or, in a few cases, to genus.
They occur on sand and rubble at the foot of slopes and in the lanes between coral heads, where there is nothing hard to attach to and being unattached is an advantage. A juvenile begins life fixed on a short stalk and breaks free as it grows. An adult that is overturned or partly buried can right itself, inflating its tissue and using tentacles and mucus to lever itself over and shed sediment, a process that takes hours rather than minutes, and the same mechanism lets it creep slowly across open sand. Heliofungia in particular is a host. The mushroom coral pipefish Siokunichthys nigrolineatus lives in groups among its tentacles and has an entry here; the same corals carry commensal shrimps, a small crab, and sometimes a film of acoel flatworms across the disc. A fungiid on open sand is worth a second look for what is living in it.
They fluoresce strongly. Under blue light with a barrier filter the fluorescent proteins in the tissue give a bright green, and in some individuals orange or red, with the septal pattern showing through as a set of radiating lines. They are among the more straightforward subjects on a fluorescence dive, partly because the animal does not move away and partly because the disc gives a flat, evenly lit surface.
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.
