Because hermit crabs do not have hard shells and their abdomens are soft and curled, they are extremely vulnerable to harm from other animals. Therefore, hermit crabs can only live in the empty shells left by some dead snails to protect their soft bodies. The abdominal limbs of hermit crabs have degenerated to only one barb, which allows them to hook the snail shell more easily, and the two large claws on the left and right can just block the exit of the snail shell to resist external enemies. However, as the body grows, hermit crabs have to change to a larger shell every once in a while. If the shell they like already has a resident, then the two sides will have a life-and-death fight, and the winner will occupy the snail shell.
Crabs keep spitting bubbles because of their unique breathing method. Crabs breathe with gills. Their gills are hidden under the hard shell and can absorb a lot of water like sponges. When they go ashore to find food, crabs breathe with the water stored in their gills, absorb oxygen, and then spit out the water and other substances. However, if they stay on land for too long, the water in the crabs' gills will gradually decrease, and they will still try to pump their gills and mouths like breathing in water, constantly absorbing the outside air, and spit out some of the water in the gills together with the air, thus forming a large number of bubbles. Crabs like to spit bubbles on land.
Sea cucumbers are echinoderms that crawl very slowly by stretching and contracting their tube feet and muscles. But don't worry, although sea cucumbers look clumsy, they have their own tricks to deal with enemies. When stimulated or invaded, sea cucumbers will spray their intestines and other internal organs from their anus, entangle the enemy, and then take the opportunity to slip away. But why don't sea cucumbers die after losing their internal organs? It turns out that there is a kind of connective tissue in the body of sea cucumbers. They are a group of cells composed of countless cells with the same shape and structure, and have super regenerative ability. Therefore, after a few weeks, sea cucumbers will grow their internal organs again.
Sea lilies are not plants like lilies on land, but a kind of echinoderms. It is just because their appearance is similar to lilies that people gave them this name. Sea lilies are the oldest species of echinoderms. There are more than 610 known sea lilies, which are divided into two categories: stalked sea lilies and sessile sea lilies. There is a long stalk in the middle of the body of stalked sea lilies, which they use to fix on the seabed. In addition, there is a receptacle on the stalk, which contains all the internal organs. Sessile sea lilies do not have long stalks, but only a few slender arms, each of which has branches and can secrete mucus. Sessile sea lilies rely on the arms and the mucus secreted on the arms to catch food.
Pearls are an ancient gemstone that is produced in mollusks such as shellfish. But why do pearls grow in the shells of shellfish? It turns out that when shellfish eat, they will open their shells. At this time, if sand or other parasites happen to fall into them, the shellfish will close their shells due to stimulation. In order to eliminate the discomfort caused by such foreign objects, their mantle will instinctively secrete a liquid called nacre to wrap these foreign objects and gradually form a solid "pearl capsule". Over time, the pearl capsule gradually increases and condenses into one or several crystal pearls. However, not all shellfish can produce pearls. As far as we know, there are only 20 to 30 species of shellfish that can produce pearls.
On the edge of the umbrella of jellyfish, there are many thin and long whisker-like strips, called tentacles, the longest of which can reach 20 to 30 meters. These tentacles are the digestive organs of jellyfish and their powerful weapons. Each tentacle is covered with stinging cells, which can eject venom. If the prey accidentally touches these venoms, it will be paralyzed. At this time, the tentacles of the jellyfish will take the opportunity to tightly grasp the prey and send it to the polyp under the umbrella. Because each polyp can secrete an enzyme that can decompose the protein in the prey, the jellyfish can quickly digest and absorb the prey.
Although starfish have no feet, their powerful "arms" can help them swim quickly on the seabed. It turns out that there are some tubes outside the body of starfish that extend like arms. They are called tube feet. The tube feet are the movement and sensory organs of starfish. There is a suction cup at the end of each tube foot. The starfish uses the movement of the tube feet and the suction of the suction cup to move on the seabed. Don't underestimate these "arms". They are not only powerful weapons of starfish, but also once they are accidentally broken, a new one will grow, and the broken part can grow into a new starfish.
There are three main theories about the cause of dinosaur extinction: catastrophic theory, gradual change theory and struggle theory. The catastrophic theory believes that 65 million years ago, an asteroid fell on the surface of the earth and caused a huge explosion, forming a dust fog that covered the sky and the sun. The photosynthesis of plants was temporarily stopped and dinosaurs could not survive. The gradual change theory speculates that 80 million years ago, the climate on Earth began to cool, causing the oxygen content in the atmosphere to decrease. Dinosaurs could not adapt to this change and could only slowly go to extinction. The struggle theory believes that at the end of the dinosaur era, a large number of small mammals fed on dinosaur eggs, which led to the final extinction of dinosaurs.
In the cold winter, food is scarce. In order to reduce physical consumption, some animals use sleep to maintain life. When animals hibernate, they enter a state of paralysis by reducing their own metabolic rate, and resume normal activities when the external environmental conditions become favorable. Hibernating animals usually start to eat a lot before the arrival of winter to accumulate body fat. But after a long winter, the nutrients accumulated in their bodies are almost exhausted. Therefore, they have to eat a lot after waking up to recover as soon as possible.
In nature, many animals live in groups, which is mainly caused by their living environment. There are many natural enemies in the living environment of animals. Only with the power of the group can they compete with these natural enemies. For example, the power of a wolf is very small, but when a group of wolves are together, even lions and tigers will retreat. In addition, group living has other functions. For example, penguins living in Antarctica usually gather together in the thousands, so that they can rely on each other's body fat to keep each other warm and resist the cold.
There is a clear sense of hierarchy among most social animals. Zoologists divide the hierarchy system among animals into three forms: single-line, circular and monopolistic. In the single-line system, the members of the group are arranged in a fixed order of rank. The second one obeys the first one, and the third one obeys the second one. No one dares to cross the line. In the circular system, the ranks of group members are constantly changing, and new individuals establish their ranks in the population through fighting. In the monopolistic system, there is only one king in the group, and the rest of the individuals are equal. Wolves are animals with a strict hierarchy.
Although animals do not communicate through written and spoken language like humans, they also have their own unique ways of communicating and transmitting information. Studies have found that animals use not only sound language but also many silent languages when communicating. For example, deer use the movement of their tails to send messages. When everything is safe and sound, the deer's tail hangs down naturally; when in a state of alert, the tail is half-raised; if danger is detected, the tail is completely upright. Most insects communicate by releasing trace substances with special smells (i.e., odor language).
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