Water Bears — Phylum Tardigrada

Tardigrades occur worldwide. Members of this phylum are often referred to as "water bears" because of their bear-like appearance and slow, lumbering gait - "tardigrada" is Latin for "tortoise-like movement." In the Arctic, tardigrades mostly inhabit freshwater and terrestrial areas, but four species – Halobiotus crispae, Pseudechiniscus suillus, Styraconyx nanoqsunguak, and S. qivitoq inhabit the Arctic Ocean.

Tardigrades are cylindrical, segmented animals with a protective coating (cuticle) over the body and extensions of the body wall that act as legs. They are often transparent, but many appear to be brown, yellow, or red depending on their intestinal contents and the pigmentation of their cuticle. Tardigrades range in size from 0.5 to 2.5 mm, but some giants can reach 17 mm! Their body is usually indistinctly divided into five segments: a head, three body segments - each bearing a pair of legs - and a caudal segment with a fourth pair of legs. Each leg ends in a claw, which may bear adhesive discs for a better grip as they walk along the substrate.

Tardigrades look and move like tiny bears!

Tardigrades usually feed on plant or animal cells, bacteria, algae, or decaying plant matter, but some species prey on small invertebrates. By piercing the cell wall or cell membrane with spiky extensions called stylets, tardigrades feed on their prey by sucking out the cellular fluid with their muscular, tube-like pharynx.

Most marine tardigrades have separate sexes and reproduce via mating, whereby males deposit sperm within the female's body to fertilize her eggs.

Tardigrades that inhabit polar waters are well adapted to the rigors of arctic life. Halobiotus crispae is sometimes found attached to brown algae during the winter and, at first glance, seems to be inactive. These animals hibernate on the algae, whereby they lower their metabolism in order to tolerate harsh winter conditions, such as freezing and lowered salt concentrations!