Miniature water bear worm. The smallest animal in the world is a creature called the miniature water bear worm. Miniature water bear worm is a multicellular invertebrate, usually only 0. 1 to 0.5 mm long. It is named "water bear worm" like a bear. Miniature water bears live in water or humid environment and can survive in extreme environment, such as high temperature, low temperature, high pressure, low pressure and radiation. Eukaryotes have complex cell structures and organs, including mouthparts, intestines, nervous system and muscles. Their bodies are composed of four pairs of legs and a cylinder, and there are many bristles on the body surface, which move in the water. The life cycle of miniature water bears is very short, only a few weeks. You can keep your body moist by absorbing water. When you are in an extreme environment, you will enter a state called "dry sleep", that is, stop metabolism until the environment becomes suitable. In dry sleep, miniature water bears can survive for decades or even hundreds of years under extreme temperature, pressure and radiation. Miniature water bears are small in size and have strong adaptability, which makes them a hot spot in biology and cosmic biology research and survive in space. Miniature water bear worm is considered as one of the creatures existing on other planets, and it is also used to study the mechanism of biological defense and life extension, as well as the application of environmental pollution and ecosystem restoration. Miniature water bear worm is one of the smallest animals in the world, with small size and strong adaptability. It is a hot spot in biology and cosmobiology research and has important application value.