A normal crab has a pair of pincers-like feet, which are called pincers' feet for digging holes, defending and attacking. The other four pairs of feet are used for walking or paddling, which are called walking feet.
The functions of pincers and walkers are different, so strictly speaking, crabs should have eight walking legs and two pincers that have no walking function. Crab's body is divided into head, chest and abdomen. There will be breastplates on the back of the head and chest, with different shapes and certain differences.
There are first and second pairs of antennae in the center of the forehead, and compound eyes with stalks on the outside. The mouthparts include 1 pair of big jaws, 2 pairs of small jaws and 3 pairs of jaw feet. There are five pairs of chest feet on both sides of the head breastplate. The abdomen is degenerated, flat and tortuous on the ventral surface of the head and chest.