Common name: Water bears

Scientific Name: Phylum- Tardigrada.

"Tardigrada" = slow walker

Description: A tardigrade is a microscopic aquatic animal. It looks like a caterpillar that has 4 pair of legs ending in claws and five body-segments. Tardigrades range is size from 0.2-0.5 mm (about the same size as a fine-led pencil dot) (Miller 1997).

Geographical range: Tardigrades are commonly found on every continent (McInnes 1994).

Habitat: Tardigrades are found in every biome including salt and freshwater environments, in humid rain forests and dry deserts, in low canyons and high altitude mountain tops. However, tardigrades are aquatic and do need to be in water to eat, breath, reproduce, and move (Miller 1997). Tardigrades are commonly found in the interstitial (water between leaves) environment of moss and lichen.

Reproduction: Tardigrades reproduce sexually and asexually. Their eggs can look like small white or bright sparkles, Christmas tree ornaments, or sea mines. It has been documented that tardigrades can produce female offspring through asexual reproduction (Miller 1997).

Input requirements (food supply): Some tardigrades are carnivores, others are herbivores or omnivores. They feed on each other, as well as mites, aphids, nematodes, and other microscopic organisms. They have a fully developed digestive and excretory system. Tardigrades do not feed during their molting periods, from a few hours to a few days (Miller 1997).

Role in the ecosystem: These microscopic creatures play a role in the cycling of nutrients.

Use as a Human Resource: To this day, no human resource use has been identified (Miller 1997).

Notes: This phylum of organism is phylogenetically located between the phylum of roundworms (nematodes) and the arthropods (crustacean, insects, ticks, and mites). In the last 200 years, since these organisms were first discovered, 3 classes, 5 orders, 15 families, 94 genera, and over 750 species have been discovered (Miller 1997).

Tardigrades are unlike any other organism because of several unusual characteristics. Tardigrades do not have a respiratory system with lungs. Instead, they breathe through their skin and pump oxygen and fluids throughout their body.

Tardigrades do not have eyes, but instead have a nervous system that responds to light sensitive spots. Tardigrades are made of 70% water. When their environment is too dry, they enter into a state of "cryptobiosis". The tardigrade shrivels up into "tun" and drastically slows down its metabolism. When tardigrades are in their cryptobiosis state they can survive temperature well below freezing, high above boiling, and under pressures of 27,000 psi (pounds per square inch) for limited time periods. These creatures can live in a state of cryptobiosis for over a hundred years (Miller 1997). One specimen from a sample of moss that was over 100 years old showed sign of life when rehydrated (Kinchin 1994). The active life of a tardigrade may only last a few months, however their lifespan may be spread over several years if they enter into a cryptobiotic state.

The tardigrade is unable to control the amount of water it absorbs through its skin. Therefore, when the tardigrade’s environment is too moist, it swells up and enters into a state called "anoxybiosis". In this state the tardigrade swells up like a balloon and floats around on the water. When the high water resides, the tardigrade deflates a little, and returns to its normal behavior of eating, moving, and reproducing (Miller 1997).