A square-bodied crab of shallow silt that watches from a burrow on eyestalks twice the height of its shell.
A small crab with a carapace clearly wider than long, squared off at the sides and usually carrying a coat of the sediment it lives in, so the colour is whatever the ground is: fawn, olive, grey or near black. The eyestalks are the character. They are very long, they fold down sideways into grooves along the front edge of the carapace when the animal is on the move or withdrawn, and they are raised together like a pair of periscopes when it is alert, which is what the common name refers to. The claws are slender and in males often conspicuously unequal in size.
It lives on sheltered shallow silt and mud, in seagrass margins and around river mouths and harbours, at depths a muck site reaches only in its first few metres. Each animal works a burrow and stays within a short distance of it. Feeding is by scooping sediment to the mouthparts, sorting the organic fraction out of it with fine setae and discarding the rest, so the ground around an occupied burrow carries small rounded pellets of cleaned sediment and those are usually seen before the crab.
Approach is what ends the sighting. The animal drops flat, the eyestalks fold, and it backs into the hole, and it returns only after a wait with no movement above it. Several species occur across the region and they are separated on the carapace ridges and the male claw, so records normally stay at the genus. Recorded from the intertidal to about 8 m.
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.
