Sand Bubbler Crab

Found sometimes in their thousands, moving at great speed, just below the high tide mark, of wave exposed mangroves, mud, and sandy areas, of estuaries and sandy beaches. These crabs leave a beautiful pattern of tiny hard pellets all over the beach, just like little bubbles, hence the name!
They feed on tiny detritus and benthic plankton.
Depth - Shoreline

These crabs build "hummocks" (little pellets of sand) around their holes before they surface from the sand at low tide. They often emerge in their thousands falling onto their backs to remove sand and then flipping back!
They then organise themselves into armies and walk forwards (unlike other crabs that walk sideways) in a straight line to the water to feed. This is done by scooping up sand and sifting out the food and then dropping off the excess as round inflated pellets.
After feeding they then dig themselves back into the sand in a corkscrew motion to await the next tide.

Brachyura crabs are considered true crabs, they have a short abdomen, four walking legs and a pair of clawed arms at the front.
Many thousands of species live worldwide in sea water, fresh water and on land.