Two spiral crowns on a coral head that vanish faster than a shutter can fire.
A serpulid worm that lives in a calcareous tube bored into living hard coral, of which the visible part is a pair of spiral crowns of feathered radioles used for both feeding and respiration. Crowns reach about 4 cm and come in almost any colour — blue, orange, yellow, white, red, brown — with the two spirals on one worm always matching. The tube is closed behind the worm by a hard plug, the operculum, which often carries antler-like spines.
The larva settles on live coral and the colony grows around the tube, so the worm and the coral head age together; a large Porites boulder can carry dozens. Withdrawal is triggered by shadow and by pressure waves and takes a fraction of a second, and the worm stays down for a minute or more, which is the whole difficulty in photographing one. The method that works is to compose and focus on a crown at a distance, wait out one withdrawal cycle without moving, and fire as it reopens — approaching closer with the camera already at the eye simply closes every worm on the head.
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.
