Tardigrades
Tardigrades are charismatic microinvertebrates that are an important component of the vast ubiquitous microscopic biodiversity that lies hidden all around us. They sometimes reach 1mm in length, but they are usually much smaller. Together with their hyperdiverse but tiny community members, tardigrades live in the soil under our feet, moss and lichens on trees and rocks, and in freshwater and marine benthic habitats from intertidal zones to abyssal depths. Also known as water bears, they have four pairs of lobopodous legs, and with a cuticle that requires molting for growth, they are part of the Superphylum Ecdysozoa with close relatives such as arthropods, onychophorans, and nematodes.
Water bears are sometimes referred to as extremophiles because they can persist under complete desiccation and other environmental extremes and survive for decades via a complex suite of biochemical tricks called cryptobiosis. They have recently enjoyed some acclaim in popular media thanks to being the only animals to survive exposure to space in low earth orbit (Erdmann & Kaczmarek 2016). With rare exceptions, though, only terrestrial tardigrades are capable of cryptobiosis, and since they are not active in times of environmental extremes even these are more accurately termed “extremotolerant.”