Mole crabs of the genus Emerentia, also known as sea lice, sand fleas or sand crabs, are small crabs that are seldom seen, except perhaps when their shells are washed up on a beach. They spend the majority of their adult lives in the sand in the surge zone on beaches, obtaining their nutrients from passing waves. They are well adapted to surviving in this inhospitable area which is constantly pounded by waves.
Mole crabs have a tough rounded exoskeleton on the upper side to deflect the force of a wave. On the underside they are able to hold their appendages close to the body, allowing them to absorb heavy impacts from waves. The coloration of the upper section varies from species to species and they have segmented antennae with a row of hairs on the underside. Some species have eyes on short stalks and others have eyes on long stalks.
On the underside mole crabs have five sets of legs which only allow them to move backwards. In addition they have a specialized digging tool known as a telson. This provides protection for the soft underbelly when in its folded position. The telson is also used to anchor them into the sand. Mole crabs can move backwards and dig themselves into wet sand in a remarkably short period of time. Females are larger than males and are typically some 4 cm long when full grown.
The genus is distributed in tropical and sub tropical areas around the world. They live in the wash zone on beaches and burrow in the sand above the wave impact zone. They are found in colonies on sandy beaches and the colonies may be spotted when the waves pull back. Their feelers make a v shaped pattern in the sand. As the tide changes so they move their position to stay in the wash zone.
Extending their feathery antennae into the water they filter plankton and detritus from the water as it washes past.
They have a short lifespan of around two to three years and can reproduce in the first year. A female can produce around 40000 eggs at a time. These are kept on the underside of the body under the telson and take around a month to develop. The eggs start off a bright orange color and as they near hatching they become a dark brown color. Once they hatch, larvae emerge and live as plankton and depending on the species can have a number of stages before morphing into adults and joining a colony on the beach.
Some species of fish and birds prey on mole crabs and they are regarded as excellent bait by fishermen for certain species of fish. Because they make relatively easy prey for birds they are more active at night. Believe it or not they are fried and eaten as a delicacy in some parts of the world.
MOLE CRAB CLASSIFICATION
IMAGES OF MOLE CRABS