One of the snapping shrimps that keeps a goby, and the arrangement is one of the most exact contracts on the reef.
The shrimp digs. It excavates and maintains a burrow in the sand, shoving loads of spoil out of the entrance with its front end, and it works at this more or less continuously because a burrow in loose sand is always collapsing. What it cannot do is see. Its eyesight is poor enough that out in the open it is helpless.
The goby can see, and it sits at the mouth of the burrow doing nothing else. While the shrimp works, it keeps one antenna laid along the fish's tail. If the goby flicks that tail, the shrimp is back underground before it has any idea what the threat was, and the goby follows it in. Both animals get a home neither could hold alone: the fish cannot dig and the shrimp cannot watch.
Hover still over a sand flat next to a reef and you will see it happening at half the burrows around you.
- light greenish body with a marbled pattern over the abdomen
- one claw enlarged into a snapping claw
- constantly bulldozing loads of sand out of a burrow mouth
- a goby standing sentry at the entrance while the shrimp works
- up to 6 cm
