There is a wealth of minuscule life forms awaiting discovery, especially in the unexplored regions of the ocean beds, mountain peaks, desserts, rainforests, topical soils and mangrove swamps. These lesser-known life forms constitute a huge new genetic resource. Soil scientists and marine biologists are studying these untapped life forms that can profoundly affect the ecology of our planet. Water bears are one such phylum of invertebrate animals. These microscopic animals have strange and exceptional morphology. They closely resemble a bear en miniature.
Water bears are commonly known as moss piglets. The scientific name is "Tardigrada" meaning "slow walker". In 1773, Tardigrades were first discovered by a German zoologist, Johann August Ephraim Goeze. Water Bears can only be seen under a high power microscope. They are mostly found in high mountains, deep sea-floor, polar regions, dunes, beaches, soil, marine or freshwater sediments, whereas, there are a few species which can be found on fresh water plants such as moss or lichen. A Water Bear has eight legs with four claws on each. It has a short, stout, cylindrical body. The mouths of Water bears have sharp objects, called stylets. Till date, 150 marine species have been documented. Tardigrades have a bear-like gait. An adult Water Bear reaches a length of 1.5 mm while the smallest can be below 0.1 mm. The newly born larvae can be as small as 0.05 mm. Water Bears molt couple of times before they reach adulthood and can be found in different colors depending on their species, including yellowish-brown, reddish, bluish and gray.
Water Bears use pointy stylets to cut moss leaves or algae for consumption. Later, they suck the juices from the plant. Tardigrades also eat nematodes and rotifers that survive on moss. Water Bears need moisture to survive. If a moss dries up, the Water Bear becomes inactive. This is known as "antibiotic state." When the moss becomes wet again, the Water Bear becomes active. Sometimes, tardigrades can exist in an antiobiotic state for over 100 years. This process is similar to hibernation adapted by cold blooded amphibians like frogs. Tardigrades can easily acclimatize to environmental stress by undergoing a process known as "cryptobiosis". It is a state in which metabolic activities come to a reversible standstill. Water Bears adopt a death-like state. They can survive extreme temperatures ranging from −273 °C to 151 °C. Water Bears can also survive without water, and oxygen for more than 10 years . These creatures can tolerate 1000x levels of X-ray radiation, boiling alcohol, thawing processes, low pressure of a vacuum and high pressure (up to 6x pressure of the deepest part of the ocean.)
Water Bears have adopted external fertilization as a method of reproduction. Female Water Bears are larger than their male counterparts. Moreover, females are more in number. They lay eggs after mating in an exoskeleton (a molt or discarded skeleton). These tiny animals are known to shed their outer sheath similar to crayfish and insect.
An experiment performed by a European Space agency revealed that Water Bears can easily survive in the space. At present, they are the only animals apart from lichen and bacteria known to survive intense radiation and low pressure. To prove the survival capacity of these tiny animals, Swedish scientist, Ingemar Jonsson from Kristianstad University along with his colleagues put dried species of Tardigrades from Kazakhstan in September 2007 on ESA's FOTON-M3 mission flight. Even after being exposed to the airless space conditions, charged cosmic rays and direct ultraviolet radiation from the Sun (known to damage DNA and cellular components), the Water Bears remain unaffected. When these Water Bears were rehydrated, they laid eggs that hatched into larvae.