There are two types of crabs: sea crabs and freshwater crabs. Among them, varieties such as flower crabs, green crabs and pike crabs live in the sea and belong to sea crabs. And hairy crabs, crystal crabs and other varieties can live in freshwater, belonging to freshwater crabs.

The body of the crab is divided into the cephalothorax and the abdomen. The back of the cephalothorax is covered with cephalothoracic armor, the shape of which varies with species. The center of the forehead is equipped with the first and second pairs of antennae, and on the outside are compound eyes with stalks. The mouthparts consist of 1 pair of large jaws, 2 pairs of small jaws and 3 pairs of jaw feet.

The cephalothoracic armor is flanked by 5 pairs of thoracic feet. The abdomen is reduced, flattened, and curved over the ventral surface of the cephalothorax. Male abdomen is narrow and long, mostly triangular, only the first two pairs of appendages are deformed into a copulatory apparatus; female abdomen is broad, each of the 2nd to 5th segment has a pair of double-branched appendages, densely covered with bristles, used to hold eggs. Most crabs are marine, with tropical shallow sea species being the most abundant.

Every 100 grams of edible part of the crab contains 17.5 grams of protein, 2.8 grams of fat, phosphorus 182 milligrams, 126 milligrams of calcium, and 2.8 milligrams of iron and rich in vitamin A and vitamin B1.

Taking the saw-edge blue crab as an example to analyze its nutritional composition:

Saw-edge blue crab is rich in protein in each component, of which the content of the female gonads is as high as 30.98%, ranking among the most protein content of fresh products. And the protein amino acid is complete, the essential amino acid score is 84.23-93.58.

Saw-margined blue crab is rich in fat and unsaturated fatty acid (UFA). The UFA of muscle reaches 74.58%, EPA is as high as 18.04%, and DHA is 13.52%. Saw Edge green crab unsaturated fat content is high, especially the human body can not synthesize omega-3 fatty acids, EPA, DHA content is high, EPA can significantly reduce serum triglyceride (TG) and cholesterol (TC) value, anti-platelet aggregation delay thrombosis, prevention and treatment of cardiovascular and cerebral vascular diseases and prostate hyperplasia, DHA can promote brain development, enhance the brain's ability to learn and remember, to prevent brain aging.