What is the difference between flat crab and swimming crab?
Flat crab generally refers to the yongjian swimming crab, also called hairy crab. The whole body is orange-red, with white spots on the large claws of the frontal region and on the swimming legs, and a purplish-red spot at the tip of the other swimming leg; the carapace width is 1.8 times the carapace length. The swimming crab's body color varies with its surroundings; the carapace is light grayish-green, with a round white spot in the anterior branchial region, the chelipeds are mostly purplish-red with white spots, and part or all of the ventral surface is white.
I. Introduction to the yongjian swimming crab
The yongjian swimming crab (is an animal of the genus Portunus in the family Portunidae. It is distributed in Japan, Sumatra, New Zealand, Australia, Sri Lanka, the coastal waters of India, Mauritius, Madagascar, and in China's Guangxi, Guangdong, Fujian and other places; its living environment is seawater, and it mainly lives on muddy and sandy seabeds at 10-100 m.
II. Introduction to the swimming crab
The swimming crab is commonly called “white crab” in some places. Because its carapace is shuttle-shaped, it is named swimming crab. There are three protrusions in the center of the shell, so it is also called “three-spot swimming crab”; it belongs to the arthropods. It is distributed in Japan, Korea, the Malay Archipelago, the Red Sea, and along most of the coast of China's mainland.
The mating season of the swimming crab in the Yellow Sea and Bohai Sea is from April to May until early winter, and along the coast of Fujian from March to April until November to December. Besides mating between sexually mature individuals, females that are not yet fully mature can sometimes also accept mating. Every year from April to May, female crabs migrate and gather in nearshore shallow sea bays or near estuaries to reproduce. The fertilized eggs produced are held on the abdominal appendages on the underside of the abdomen. Each female crab can lay eggs 2-3 times during the breeding season, with a total of about several hundred thousand to two million eggs. Newly laid eggs are yellow, and after about 2 weeks they turn dark brown. They hatch into zoea larvae, which live as plankton, with a total of 5 stages; after molting at the 5th stage they enter the megalopa stage, and after 1 more molt they become juvenile crabs, going through more than 20 molts from small to large. The general lifespan is about 3 years. The three-spot swimming crab grows very quickly, and its maximum weight can reach 0.5 kg.