The horseshoe crab is a national second-class protected animal can not be eaten.

The ancestors of horseshoe crabs appeared in the geological history of the Paleozoic era of the Devonian period, when dinosaurs have not yet appeared, the primitive fish has just been introduced, with the passage of time, and its contemporaries or evolution, or extinction, and only horseshoe crabs from more than 400 million years ago to date, still retains its primitive and ancient appearance, so horseshoe crabs have a "living fossil" called "living fossil". "

The earliest known species of horseshoe crab is the horseshoe crab.

The earliest horseshoe crab fossils were found in the Ordovician period (505 million to 438 million years ago), and the fossils of horseshoe crabs with a morphology similar to that of modern horseshoe crabs appeared in the Jurassic period (208 million to 144 million years ago).

As old as trilobites (now only fossilized). ***4 species found in Asia and on the east coast of North America. Also known as the horseshoe crab, but not a crab, but related to scorpions, spiders, and the extinct trilobites.

Relationship to humans

Humans have long used horseshoe crabs for food, and their meat, gonads, and eggs are edible. However, their blood contains too much copper, so they can be poisoned if eaten in excess. In addition, round-tailed horseshoe crabs contain highly toxic tetrodotoxin and should not be eaten.

It has been found that the compound eyes of horseshoe crabs have a kind of lateral inhibition phenomenon, that is to say, it can make the image of the object (especially tracking the dynamic image in the background) clearer, and this principle has been applied to the television and radar system, which improves the clarity of the television imaging and the sensitivity of the radar display.

The blood of horseshoe crabs, which is blue in color, contains copper ions (hemocyanin). An extract of this blue blood, the "horseshoe crab reagent," can accurately and quickly detect whether the body's internal tissues are diseased by bacterial infection.

It is used in the pharmaceutical and food industries to monitor for toxin contamination. Metastatic cells in the blood (small amounts, centrifuged to obtain a precipitated white substance) have even been taken into outer space to detect organisms and protect astronauts from disease.

The above reference? Baidu Encyclopedia - Horseshoe Crab