Water bears, also known as tardigrades, are a type of microscopic animal that can be found in nearly all types of environments across the globe. They are one of the most resilient creatures on Earth, able to withstand incredibly harsh conditions that would kill other organisms. Water bears have been known to survive temperatures as low as -328 degrees Fahrenheit and as high as 300 degrees Fahrenheit, pressures six times greater than those found at the bottom of the Mariana Trench, ionizing radiation at doses thousands of times higher than what would kill a human, and even the vacuum of outer space.
Despite their hardiness, water bears are very delicate creatures that require specific conditions to thrive. They typically live in moist environments such as mosses or lichens, but can also be found in soil, freshwater sediment, and even on the surface of plants. When conditions become too dry for them to remain hydrated, they will enter into a state of cryptobiosis – a type of suspended animation in which they drastically reduce their metabolism and lose up to 97% of their body water content. In this state, they can remain alive for decades until moisture becomes available again.
Water bears reproduce both sexually and asexually. The vast majority of young are born alive through parthenogenesis (asexual reproduction), but sexual reproduction does occur occasionally when two water bears come into contact with each other. During sexual reproduction, the male will insert his retractable penis into the female’s vagina and deposit sperm inside her body cavity; fertilization then occurs internally. After fertilization has taken place, the female will produce an egg sac containing anywhere from 8 to 40 eggs which she will then carry around with her until they hatch roughly two weeks later. Once hatched, juvenile water bears look like miniature adults and are able to begin reproducing themselves within months.
Water bears have simple nervous systems consisting only of a brain ganglion connected directly to their muscles; however recent studies suggest that they may be more sophisticated than previously thought. They seem to exhibit primitive forms of learning and memory retention which allows them to adapt quickly to changes in their environment – something that is critical for survival given their ability to enter into cryptobiosis when necessary. Additionally, some species of water bear have been shown to possess genes similar to those found in humans that allow them repair damage caused by UV radiation exposure – making them potentially useful models for studying ways to protect against harmful effects from solar radiation exposure here on Earth