Some tardigrades have three tubular glands associated with the rectum; these may be excretory organs similar to the Malpighian tubules of arthropods, although the details remain unclear.The tubular mouth is armed with stylets, which are used to pierce the plant cells, algae, or small invertebrates on which the tardigrades feed, releasing the body fluids or cell contents.They were first discovered by the German zoologist Johann August Ephraim Goeze in 1773.The name Tardigrada (meaning "slow stepper") was given three years later by the Italian biologist Lazzaro Spallanzani.The mouth opens into a triradiate, muscular, sucking pharynx.The stylets are lost when the animal molts, and a new pair is secreted from a pair of glands that lie on either side of the mouth.
Newly hatched tardigrades may be smaller than 0.05 mm.
When collected, they may be viewed under a very low-power microscope, making them accessible to students and amateur scientists.
Johann August Ephraim Goeze originally named the tardigrade kleiner Wasserbär (Bärtierchen today), meaning "little water bear" in German.
Mating occurs during the molt with the eggs being laid inside the shed cuticle of the female and then covered with sperm.
A few species have internal fertilization, with mating occurring before the female fully sheds her cuticle.