What is the magical crab family like?

Crab has many functions such as submarine, dredger and garbage disposal, and it is a wonderful creature in nature. From the perspective of 180, crabs can change their shell color according to the 24-hour "clock" in their bodies. You can regrow the lost periscope, or break its limbs and escape; Can identify compounds far away; It can also use its breathing system in reverse at will, so it can not only breathe on water or underwater, but also breathe in soil or sand. There are about 4500 kinds of real crabs in the world, and they all have these skills.

Crab is a common name for decapod crustaceans. Decapoda includes shrimp, lobster, hermit crab and real crab. The size of real crabs varies greatly, and adzuki bean crabs are only 6 mm long; The foot span of the giant spider crab is 1.5 meters.

In an emergency, crabs will use ingenious physiological structures to escape from danger. Ten limbs of the crab were broken early. If a limb is bitten by a carnivorous fish, or injured, or caught in a stone crack, it will immediately contract a special muscle, break the limb, and then run away, while the enemy will focus on dealing with the still twisted limb. Crabs don't even bleed when they cut off their limbs, because there is a special membrane in their limbs, which completely blocks nerves and blood vessels. In addition, there is a special "door" to close the rest. At the same time, blood cells immediately supply lipid protein and begin to grow new limbs.

For self-reproduction, female crabs lay about 6.5438+0.85 million eggs at a time, and some females lay more than 6.5438+0.000 eggs at most. Crab eggs hatch quickly, and after a few hours, they become short-helmet-shaped Daphnia larvae with two prominent big eyes. After 3 months, it turned into a big eye, and the crab shape appeared roughly. A few weeks later, the big-eyed young crab swam to shallow water and became a young crab. Since then, it has spent all its life at the bottom of the sea. Adult crabs are crustaceans and decapods. It has two branchial chambers, and each branchial chamber has six channels, namely 10 slender cracks at the upper end of the leg and two interconnected grooves. Water is pumped into the gill chamber through a hairy paddle on the head. It also has a sweeper, called an appendage, which constantly removes impurities from the gills.

100 Many biologists have been studying and observing crabs for many years, but there are still many questions that cannot be answered satisfactorily. For example, many crabs have a biological "clock" that can make the color of crab shells change regularly. It is found that there are three pigments on the crab, red, white and black, and two pigments are scattered on the shell during the day. At night, the colors of hypopigmentation turn pale. This biological phenomenon cannot be explained. Crabs have a special ability to tell directions. Some crabs use celestial bodies to analyze polarized light to determine the direction under water, which is also difficult to explain. Another example is that crabs have a pair of special compound eyes with a viewing angle of180; There is an eye stalk under the compound eye, which is hidden in the hard eye socket on the carapace and can be extended independently. If you break an eye, it will soon grow a new one. What people can't explain is whether the crab's eyes and eyestalks are completely damaged or cut off, so it no longer grows with its own eyes, or it can only grow an extra antenna in its eye socket. Biologists also found that the arterial blood pressure of crabs is only 1/20 of that of humans, so the arterial blood vessels are large, so there will be no hypertension and no death from heart disease. But why do some crabs have an auxiliary heart under their gills, just to help blood circulation?