Emerita is a small genus of decapod crustaceans, known as mole
crabs. These are small animals that burrow in the sand in the wash zone and use their antennae for filter feeding.
Emerita is adept at burrowing, and is capable of burying itself completely in 1.5 seconds. Unlike mud shrimp, Emerita burrows tail-first into the sand, using the pereiopods to scrape the sand from underneath the body. During this action, the carapace is pressed into the sand as anchorage for the digging limbs. The digging requires the sand to be fluidised by wave action, and Emerita must bury itself in the correct orientation before the wave has passed in order to be safe from predators.
As the tide changes, Emerita changes its position on the beach; most individuals stay in the zone of breaking waves. This may be detected by the physical characteristics of the sand. As the tide falls, the sand is allowed to settle; when Emerita detects this, it uses the temporary liquefaction from a breaking wave to emerge from its burrow, and is carried down the
beach by the wave action. Longshore drift may also drag Emerita laterally along a beach.
Emerita has a short life span, perhaps no more than 2–3 years, and can reproduce in its first year of life. The eggs are bright orange, and hatch into larvae, which may live as plankton for more than 4 months and can be carried long distances by ocean currents. The number of zoeal stages varies between species from 6 to 11.