Emerita (crustacean)
Emerita is a genus of small, burrowing sand crabs within the family Hippidae. These crustaceans are commonly known as mole crabs, sand fleas, or sand crabs, although the name "sand crab" is also applied to other similar crustaceans. Emerita species are found in sandy beaches in temperate and tropical regions worldwide.
Description
Emerita crabs are adapted for life in the dynamic intertidal zone of sandy beaches. They possess a streamlined, barrel-shaped body, which allows them to efficiently burrow backwards into the sand. Their carapace is smooth and oval, and typically ranges in color from grayish-white to tan, often blending in with the surrounding sand. A key characteristic is the presence of feathery antennae, which they use to filter plankton and other organic matter from the receding waves. They lack the prominent claws (chelipeds) of many other crab species, instead possessing modified appendages suited for digging and feeding.
Habitat and Distribution
Emerita species inhabit the swash zone of sandy beaches, the area that is repeatedly covered and uncovered by waves. Their distribution is influenced by factors such as wave energy, sand grain size, and temperature. They are commonly found in large aggregations, where they burrow in the sand to escape predators and desiccation during low tide. Their global distribution includes coastlines in the Americas, Africa, Asia, and Australia.
Behavior and Ecology
Emerita crabs are filter feeders, using their antennae to capture plankton and detritus from the water column as waves wash over them. They are highly mobile within the swash zone, constantly adjusting their position to maintain a location where they can access food. Their ability to burrow rapidly allows them to avoid being swept away by strong currents or preyed upon by shorebirds and fish. They play an important role in the beach ecosystem by consuming organic matter and serving as a food source for other animals.
Reproduction
Emerita crabs have separate sexes. Females are typically larger than males. Reproduction involves internal fertilization, with males transferring sperm to females. Females carry the fertilized eggs on their pleopods (abdominal appendages) until they hatch into planktonic larvae. The larvae undergo several developmental stages before settling and metamorphosing into juvenile crabs.
Species
The genus Emerita includes several species, some of which include:
- Emerita analoga (Pacific mole crab)
- Emerita asiatica
- Emerita austroafricana
- Emerita benedicti
- Emerita brasiliensis
- Emerita emeritus (Indo-Pacific mole crab)
- Emerita holthuisi
- Emerita karachiensis
- Emerita rathbunae