Marine Biology (2+1)

Emerita asiatica

Species: E.asiatica

Family : Hippidae

Common name : Mole crab / sand crab

Habitat : Sandy shores

Body symmetrical and almost cylindrical. A pair of stalked eyes. The first pair of pereopods is without subchelae in the family Hippidae (but in the family Albunidae the first pair of pereopods possesses subchelae). The telson is very long and lancet shaped, reaching the mid ventral part of the body.

Fairly prolific little crab, dark gray in colour (specimens occurring along Kanyakumari waters appear light pinkish and little larger in size). Lives in colonies inter-tidally in coarse sand at the edge of the surf zone on beaches. The egg shape and the smoothness of the body ideally suits its burrowing habit, a contour that is efficient for dwellers in shifting sands where the surf is high and its pressure is distributed too evenly to throw the animal out of balance. While the true crabs (Brachyura), could characteristically move in any direction i.e. forward, backward or sideways, the mole crab (Anomura) whether swimming, crawling or burrowing, it moves backwards only.

The backward borrowing movement through the loose moving sand grains in the surf zone is rapid so that it can burrow out of sight in a flash. It is sometimes disturbed from its hiding place under the sand by a retreating wave and so exposed to view for a brief period that lapses before it can bury itself again, which it does with great rapidity. Trying to catch one can be very frustrating. Like little darts of porcellaneous china they slide between fingers and hands, zipping this way and that. It feeds by using its four hairy attennae, which protrude from below its eyes. These antennae are projected from the sand and rotated, creating a current that directs small planktonic organisms towards the hairy mouth parts. The eggs are yellow and carried under the female’s abdominal flap, which is folded beneath the carapace.

E. asiatica actively breeds during April to June along the East coast. The free – swimming larvae settle to the bottom and grow into small specimens of the adult form.

Size : 40mm