All Tardigrades (Water Bears)

Tardigrades, or water bears, are small, bilaterally symmetrical animals averaging 0.1 to 0.5 mm long, with four pairs of legs ending in adhesive pads, discs or claws. The uncalcified cuticle is made of up to seven layers of proteins and chitin and is shed as the animal grows, with sexual maturity reached after three to six instars. They walk with a stepping motion, although at least one marine species swims by expanding its cuticle like the bell of a jellyfish. Their most distinctive behavior is entering cryptobiotic stages, including encystment, cryobiosis and anhydrobiosis, in which metabolic activity is greatly reduced or shows no outward sign at all.