It lives on its own dinner.
This fish spends its life among the arms of a feather star, gripped to a stalk or lying along an arm, colored to match whichever one it has chosen. And what it eats is the feather star: the pinnules, the fine side branches that make each arm look feathered, cropped off one at a time.
That is an unusual arrangement even by reef standards. Most animals living on a host either pay rent, in cleaning or in defense, or at least take nothing from it. This one is a lodger that eats the building, slowly, in amounts the crinoid can regrow, and gets protection out of the deal on top: a feather star is a thicket of sticky, unpleasant arms that most predators leave alone, and a four-centimeter fish inside one is effectively unreachable.
Finding it means looking at crinoids properly rather than past them. Dark reddish with four yellow lines running the length of the body and yellow dots scattered between, on an animal the size of a fingernail, in a tangle of arms of exactly the same color.
There are usually shrimps and brittle stars in there too, on the same terms.
- dark reddish with four yellow lines and yellow dots scattered between them
- almost always on a feather star, matching its arms
- flattened underside with a sucker disc, so it rests rather than hovers
- up to 4.5 cm
Why it's threatened
There are no known major threats.
Threat classification from the IUCN Red List.
