Horseshoe crab is the only species on the earth that has lived for more than 400 million years and still retains its original appearance. As a leader who survived the four mass extinctions, horseshoe crab has survived the "darkest period" of biological extinction on the earth and has super survival ability.

In its heyday, there were hundreds of species of horseshoe crabs. With the intensification of human activities, habitat destruction and overfishing, there are only four species of horseshoe crabs in the world, namely American horseshoe crabs distributed from the east coast of North America to the Gulf of Mexico and Chinese horseshoe crabs, southern horseshoe crabs and round-tailed horseshoe crabs in Asia.

Chinese horseshoe crab

The Chinese horseshoe crab is 60 cm long and weighs 3-5 kg. The horseshoe crab consists of three parts: the head and breastplate are slightly horseshoe-shaped (hence the name horseshoe crab), the abdomen is hexagonal with spines on both sides, and the tail is a long tail sword. Limulus is like a crab, bigger than it. Although they all have joint appendages, the relationship between horseshoe crab and horseshoe crab is far less close than that with spiders.

The first pair of appendages of horseshoe crab and spider are chelated. All have four pairs of feet, which are taxonomically called chelated animals. The main difference between horseshoe crab and spider is that horseshoe crab has many spines at the base of its appendages and surrounds its mouth to chew food, so it is also called arthropod.

Limulus is an ancient creature, which lived on the earth as early as Devonian more than 300 million years ago, and still maintains its shape. It can be called an ancient adherent in the ocean, and it is an animal of the same period as trilobites. When primitive fish just came out and dinosaurs didn't rise, horseshoe crab was a prosperous marine resident in Devonian (Permian 225 million years ago) 395-345 million years ago.