Undersea mandarin duck

There is a large arthropod that grows along the coast of southern China and Japan. It looks like a scoop. The male and female are inseparable all day long. They walk, eat, and rest together with their hooks. This is the horseshoe crab that people call the "undersea mandarin duck." Horseshoe crabs live on the sandy bottom and eat worms, shellless molluscs, and some marine plants. Rest during the day and active at night. The back of its cephalothorax is bulging, its ventral surface is concave, and there is a hard tail behind it, which looks like a melon gourd with a handle. Every summer, it swims from the deep sea to the offshore sea, climbs up to the beach in pairs, and uses its well-developed legs to dig holes and lay eggs. It moves clumsily and is easily caught on the beach.

The eyes of the horseshoe crab are compound eyes composed of 1,000 small eyes. There are interlaced lateral nerve connections between the small eyes, making it easy for the horseshoe crab to see objects clearly, and to accurately hunt prey or effectively escape from enemies. In addition to a pair of compound eyes, it also has a pair of small central ommatidia. A scientist once won the Nobel Prize in Physiology by studying the electrical impulses of the optic nerve of horseshoe crabs and revealing the principles of the functions of various visual systems. Limulus blood can be used to detect endotoxins in the human body. Bacterial endotoxins can cause poisoning and shock when they invade the human body. A reagent made from Limulus blood can quickly detect the content of endotoxins with extremely high sensitivity. If 10,000 tons of distilled water contains one gram of endotoxin, the Limulus reagent can also detect it. Therefore, this reagent is very helpful to doctors in diagnosing certain diseases and has been widely used in medicine.

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