Crab

Introduction

Crab any of the members of decapod crustaceans belonging to the suborder Brachyura with a broad, rather round, upper carapace and a small abdomen tucked beneath the body living in marine, brackish, or freshwaters. In the world 133 species of crabs contains. Though they differ from species to species in size, shape, colour and structure, they closely resemble each other in general morphology and biology. Sixteen species of crabs have been so far reported from Bangladesh waters, of which the common ones are Scylla serrata, Portunas pelagicus, P. sanguinolentus. The six important genera used as food crabs are Scylla, Portunus, Charybdis, Matuta, Varuna and Sartorina. Most of these species are economically important but the serrated mud crab, also known as mangrove crab, or Scylla serrata is now the most commercially important species and is widely distributed in the Indo-Pacific region, including the bay of bengal. Bangladesh earns about US $ 6 million per year by exporting 1,500 m tons of live mud crab to Singapore, Hong Kong, China, Taiwan and Japan.

Distinguishing Characteristics of Mud Crab (Scylla serrata)

1. The segmentally organised body of crab is divided into a well-developed cephalothorax, and a highly reduced abdomen with six cephalic, eight thoracic and six abdominal segments.
2. Each segment except the first bears a pair of uniramous or biramous appendages.
3. There are five pairs of legs used for running, swimming, jumping, climbing and burrowing.
4. Crabs construct burrows of different shape and size mainly for concealment but mud crabs use those also at the time of molting and breeding.
5. Crabs can breed throughout the year, but for mud crab peak seasons in Bangladesh are May to August, and December to February.

Systematic Position of Mud Crab

Phylum: Arthropoda

  Class: Crustacea

     Order: Decapoda

        Family: Grapsidae

          Genus: Scylla

             Species: Scylla serrata

English Name: Green crab \ Mangrove crab

Differentiating Sexes

As juveniles, male and female mud crabs are difficult to differentiate. However, differences between the sexes become more apparent as the crabs mature. The abdominal flap of females is much broader than that of males and becomes heavily pigmented when the female reaches maturity. Another obvious difference between the sexes is in the claws, which are much larger in males than in females.