A crinoid is a habitat before it is an animal, and three or four species live in it.
A crinoid, and among the oldest body plans still swimming: a small central disc with a mouth on the upper surface, a ring of feathered arms held out into the current to filter plankton, and a set of short curled cirri underneath that grip the substrate. Colour runs the whole range — black, yellow, red, green, cream, and combinations of them — and the animal will detach and swim, with a slow alternating beat of the arms, to move between perches.
Its place on this list is as habitat. A single feather star routinely carries the squat lobster Allogalathea elegans, a Laomenes shrimp, a small clingfish and sometimes a juvenile ghost pipefish hanging beside it, all coloured to match the arms of that particular host. Searching one is done with a light held off to the side, looking for stripes that run at the wrong angle to the arms. Recorded from the shallows to about 40 m, most abundant where there is current. The arms shed easily and regrow; a crinoid moved by hand loses arms, which is reason enough not to move one.
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.