A gray-brown goby with a big first dorsal fin it raises like a flag, dark-blotched and edged in yellow, on silty sand where the visibility is usually poor. Up to 8 cm (3.1 in), and permanently stationed at the mouth of a burrow it did not dig.
The burrow belongs to a snapping shrimp, and the arrangement is one of the best-known partnerships on the reef: the shrimp digs and maintains the tunnel for both of them, the goby stands guard. The shrimp is nearly blind, so it keeps one long antenna in contact with the fish at all times while it works, and a flick of the goby's tail sends both of them underground.
The signals are more specific than they look. Different tail movements mean approach, threat and retreat, the shrimp responds correctly to each, and pairings are consistent enough that particular goby species keep company with particular shrimp species. Neither animal does well alone: the shrimp will not leave a burrow without a partner, and the goby has no way to build one.
- tall first dorsal fin with a large dark blotch and a yellow margin, raised like a flag
- gray-brown body with pale bars and blue-white speckles on the cheek
- a shrimp working at the burrow entrance beneath it
- length up to 8 cm
