The horseshoe crab is an arthropod whose form is close to that of a crab, and is more closely related to a spider. It belongs to the phylum of arthropods in zoology, with the subphylum of stinging limbs, limb stomatopods, sword-tailed order, the length of the body is generally about 1~2 feet, the weight of the big ones can reach 8~9 pounds. Its appearance is very strange and ugly, so people often call it "ugly monster" or "sea monster".
According to paleontological historians, horseshoe crabs have a long history. As early as in the geological era of the "Paleozoic" of the "Devonian", horseshoe crabs and brachiopods of the ancient creatures of the sea bean sprouts at the same time, has a history of 350 million years. Horseshoe crabs were already very old when dinosaurs first appeared on Earth. Dinosaurs suddenly and mysteriously went extinct 65 million years ago, while horseshoe crabs survived to this day. Some scholars believe that horseshoe crabs probably evolved from trilobites, because during the embryonic development of horseshoe crabs, they go through a trilobite larval stage, especially when it just comes out of the egg shell before molting, much like trilobites. Paleontological historians are surprised: from the "Devonian" since the 350 million years, the horseshoe crab form has not occurred what is more significant changes. Therefore, paleontologists call horseshoe crabs "living fossils" or "living paleontology".
The blood of horseshoe crabs is blue. In ancient times, when science was not well developed, this was a longstanding mystery. It is only in recent times that scientific research has finally unraveled this mystery: the basic color of blood is determined by the mineral composition contained in the blood. Because of the horseshoe crab's blood to copper as the oxygen carrier, contains hemocyanin, hemocyanin does not contain iron but copper compounds, and therefore blue.
Horseshoe crabs, however, have another mystery that has baffled scientists, and that is their rather complex and peculiar visual system. In addition to a compound eye on each side of its head, it has a pair of single eyes in the center of its head that are connected together. But these four eyes don't rotate, and each has about 1,000 small eyes, which are larger and have thicker nerve fibers. Currently, scientists only know that light can help horseshoe crabs determine the direction of action, but the entire visual system in the horseshoe crab's actions play a role in how? It's still a mystery that hasn't been fully solved yet.
Studying the structure and function of the horseshoe crab's eyes will help scientists study how the human eye perceives the boundaries of lines and can compare objects and colors with each other. The study of the eye's response to such light stimuli, but also help to analyze the causes of many eye diseases that lead to total blindness, which is conducive to determining the method of treatment, for the study of human eye diseases and their prevention and treatment methods are very enlightening and reference value. Therefore, the visual system of horseshoe crab has become an important research object of modern e-bionics.
The eyes of horseshoe crabs are like the most sensitive electromagnetic wave receivers, which can receive extremely weak light in the deep sea, so that horseshoe crabs live in the deep seabed but never lose their direction. Many scientists believe that the horseshoe crab's pair of compound eyes have the effect of light side inhibition, which can enhance the contrast of the image viewed, making the fuzzy image become clear. This inspired scientists to apply the principle of lateral inhibition to design a new television camera that would improve the clarity of television.
In recent decades, many scientists have conducted long-term in-depth exploration and research on the visual system of horseshoe crabs, and have achieved promising results. For example, Dr. Kefir Hartline, a famous scientist at Rockefeller University in the United States, won the 1967 Nobel Prize by conducting comprehensive and systematic explorations and research on the electrical impulses of the optic nerve of the horseshoe crab, revealing many principles about the function of various visual systems.
However, many of the mysteries of the horseshoe crab's visual system have yet to be further studied and explored by scientists.