In almost every shrimp in the sea the rostrum, the spike between the eyes, is a fixed part of the shell. It is welded to the carapace and it does not move, any more than your nose does.
In this family it is hinged. The rostrum is jointed at the base and the animal can raise and lower it, which is where the names hingebeak and Rhynchocinetes, moving beak, both come from. Nobody has fully settled what it is for; the plausible answers involve feeding and combat.
Combat matters here, because in this genus males grow through a series of forms. Small males look much like females; the largest carry hugely enlarged front claws and use them in shoving contests over access to females, which happens in the hours after a female molts and can be mated. The result is a group in one cave containing what look like two or three different species.
By day they pack into caves and crevices in dozens, red and white and hard to count, and after dark they come out to scavenge.
- translucent body under red and white lines, with scattered white spots
- a Y-shaped white mark on the front of the carapace
- rostrum hinged at its base, and it can be raised and lowered
- large black eyes; usually in dense groups inside caves
- up to 4 cm
