All crabs are decapod crustaceans, which simply means they have 10 legs. Eight of these legs help in the movement (walking legs) and the first two, called claws or chelipeds (chela means 'claw' and ped means 'Foot'), in capturing prey, communication, mating and defense. The nearest relation to the decapod crabs are the anomuran crabs, which have only 3 pairs of walking legs. A typical example for the latter is the hermit crab that has a soft coiled abdomen protected by a snail shell.
Crabs are usually aggressive towards each other, and males often fight over females. Social and mating behaviors are complex. Many make species - specific sounds by banging on the ground with their pincers or stamping with their feet, or make elaborate pincer movements. Mating occurs only when the female has just moulted and her new shell is not yet hard; the males however are in their hard-shelled form. Thus males may protect a female just before she moults, so he can have first access when she is able to mate, and may continue to protect her till shell hardens. Some males even carry the female around.
The Crab meat is very tasty and nourishing. Crab curry is a reputed cure for asthma. Similarly soup made from the swimming crabs Portunus sanquinolentus and P. pelagicus is commonly used by people just after recovery from malaria and typhoid. Scylla serrata serves as a cure for diarrhorea and dysentery.
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