Water bear (Macrobiotus sapiens) in moss. Color enhanced scanning electron micrograph (SEM) of a water bear in its active state. Water bears (or tardigrades) are tiny invertebrates that live in aquatic and semi-aquatic habitats such as lichen and damp moss. They require water to obtain oxygen by gas exchange. In dry conditions, they can enter a cryptobiotic state of desiccation, known as a tun, to survive. In this state, water bears can survive for up to a decade. This species was found in moss samples from Croatia. It feeds on plant and animal cells. Water bears are found throughout the world, including regions of extreme temperature, such as hot springs, and extreme pressure, such as deep underwater. They can also survive high levels of radiation and the vacuum of space. Magnification: x250 when printed 10cm wide.