There are many crab species existed in this world. They comprised five pairs of leg with exoskeleton body. There are over six thousand species of crab living around the world including marine crabs, freshwater crabs, and terrestrial crabs. One of the marine crab family is family Portunidae from the order Decapoda. There are five genera from this family that can be found in Malaysian water such as Portunus spp., and Thalamita spp.
Crabs are ten-legged organisms that walk sideways. The first pairs of their legs are known as claws and the last pairs of their legs are known as swimming legs due to its paddle-shaped. Marine crabs are scavengers and bottom-dwellers where they primarily feeds on worms, clams, mussels, other crabs and other invertebrates. They mostly can be found at the coastal areas and also sandy rocky areas. They undergo stages of moulting for their growth by changing their skeleton.