Hovers vertically above a burrow it lines with shell and rubble, and drops in tail first when approached. Males brood the eggs in the mouth and air them by spitting the ball out and taking it back.
To about 12 cm, pale blue-grey with a yellow head and large eyes set high, and a body that is mostly tail. It hovers vertically above its burrow with the tail still in the hole and drops straight back in, tail first, when anything comes too close.
The burrow is a construction. The fish digs it, lines it with shell and coral rubble carried in the mouth one piece at a time, and rebuilds it constantly, so watching one burrow for a few minutes shows the whole business of running a household. The male broods the eggs in his mouth, and airs the ball by spitting it out and taking it straight back in, which lasts about a second and is the photograph everybody wants. It happens more often early in the morning. Getting close is a matter of settling on the bottom several metres back and waiting for the fish to come back up, because a jawfish that has gone down while you were moving will stay down.
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.