Print This Page

 Major Groups | Tardigrada (moss bears)

Tardigrada (moss bears)

Tardigrades are commonly called “moss bears” referring to their stout body, stumpy legs and the habit of many species to live in the water film of mosses. Tardigrade means “slow walker”, aptly describing their slow sluggish movement.

Descriptive Features:

  • multicelled animals
  • head more or less distinct, with a pair of eyes
  • 5-segmented body short and stout, covered by a thin cuticle which may be smooth, ridged or variously sculptured
  • 4 pairs of stumpy, unjointed legs, each with 4 terminal claws
  • Total length: tiny animals, 0.2 - 0.5 mm

    Distribution: Australia wide

    Sensitivity Rating: none

    Functional Feeding Group: macrophyte piercer


    Mt Buffalo Vic

    Ecology: All tardigrade species are aquatic in the sense that they live in the surface waters of mosses, liverworts and sometimes larger plants (limno-terrestrial). Some species are more truly aquatic being found closely associated with ponds, small lakes and in slow flowing areas of rivers. They live on the surface of mud, detritus and submerged vegetation. Moss bears move by sluggish crawling, feeding on cell sap by inserting a pair of anterior stylets into plant cells.
    Tardigrada grow by moulting through a series of instars, increasing in size but maintaining a similar form. The cuticle is moulted four to six times during the life of an individual. They can live actively for only a few months but the actual life span may be several years if there are cryptobiotic periods. Cryptobiosis occurs to resist desiccation and temperature extremes for very long periods. When environmental conditions become unfavourable, tardigrades retract their head and legs, become wrinkled, desiccated and body activities cease. In some species, a resistant cyst wall is also formed beneath the wrinkled cuticle.
    The majority of moss bears are females; males are unknown in some genera (females produce females without fertilization) so reproduction is both sexual and asexual. Two types of eggs are produced. A thin shelled egg is produced under normal conditions and needs no fertilization. A thick shelled egg is produced at the onset of unfavourable environmental conditions and may be fertilized. Eggs are attached to the substratum singly or in groups, or sometimes eggs are left within the discarded cuticle of the female after a moult. Eggs may be smooth, have rounded projections or thin spines. The egg form is taxonomically specific. Eggs hatch to miniature adults.


    Information Sources: Williams 1980, Miller 1997, ABRS 2004