The sand crab's food supply comes solely from plankton and its important component, dinoflagellates. To feed, the crabs find the swash zone where the waves are breaking and bury themselves backwards. Then they use antennae to catch plankton during a receding wave.
With their faces pointed to the sea, the crabs unfurl a pair of feather-like antennae that catch plankton. The action of the feather-like antennae is so fast that a crab can feed multiple times during one receding wave. The dinoflagellates that the crab eats are single-celled organisms that have chloroplasts mitochondria and nucleus and are covered by plates.
Sand crabs are about the size of a human thumb and live in shifting sands on beaches and sand dunes. It has a gray shell, which keeps it camouflaged and a thick, armored body with pin-like legs that help it walk on shifting sand. Unlike most crabs which can move forward, backward and sideways, the sand crab can only move backward. It also has no claws on its front legs, unlike most species of crab.
Sand crab are fed on by birds and fish and are used as bait to catch surfperches. Bait fisheries use sand crabs that are in their soft-shell stage after molting and before the new shell hardens.