SOLDIER CRABS ON DUTY

Imagine you are a soldier crab (Mictyris longicarpus) that lives in the inter-tidal zone along the east coast of Australia. Your job is to avoid getting eaten by shore birds while scouring the sand at low tide and cleaning it of detritus, like an army of vacuum cleaners.
You have been hiding in the sand under the water - up to 2 metres deep. Your temporary refuge has been a bubble of air (about 4 times your body volume) that you created around yourself as you quickly burrowed down in a clockwise corkscrew motion, by walking backwards with your right legs.
Now that low tide has occurred there's no time to waste -
Call the muster! Form into rank! Forward march! It's just as well you're not like other crabs - imagine the pathetic army with soldiers that could only walk sideways!
Hang on a minute. How are you supposed to complete your tour of duty if you keep breaking rank to run off and wet your gills like other crabs? No problem. You have been designed with not only gills but also lungs, adjacent but distinctly separate, to provide you with 90% of your oxygen requirements. In fact you are even capable of absorbing oxygen through the decalcified joints of your legs and absorbing moisture through the silky hairs on your abdomen. No toilet stops, drink breaks or even breathers for you!
What a very cleverly designed little soldier, and smart...
Without tide-tables, calendar and watch, you even know when the next low tide is due.
Wherever did you get your sense of time from?

Acknowledgements:

David P. Maitland, Arthur Maitland, Caroline Farrelly, Peter Greenaway, University of NSW
Photo credit: Tony Sullivan