Tardigrades, often referred to as “water bears,” are classified in the phylum Tardigrada. They have lobopodous legs, and most are 250-500 µm in length as adults.1,2 The habitat of these small animals ranges from sea to fresh water to land, and they have been collected from ocean depths of 4,960 m to altitudes of 6,600 m in the Himalayas.1,2 The number of species is said to exceed 800.3

All tardigrades, however, must be active in water, even terrestrial species. For this reason tardigrades are fundamentally defined as aquatic animals. Terrestrial tardigrades inhabit microenvironments such as in lichens, mosses, soil, and leaf litter, and in such environments they are often exposed to periods of dehydration. In these environments, tardigrades often suspend any activities. This state of suspended activity is called cryptobiosis, and it is a characteristic strategy of terrestrial tardigrades.