TARDIGRADE LIFE

Naked Eutardigrades hatch as small versions of the adults and grow by molting through instars that are similar but larger. The armored Heterotardigrades change from one molt to the next, achieving their distinctive morphology as adults. Changes include the number and size of dorsal spines, texture of plates, and the appearance of the gonopore.

The active life of a tradigrade may last only a few months, although it may be spread over several years if interrupted by cryptobiotic periods. Growth and molting occur throughout the active life and from six to 12 instars are common (Higgins 1959). Molting begins with the 'simplex' stage where the feeding apparatus is lost. The old cuticle is shed and left behind. Then a new feeding apparatus is regenerated. Tardigrades do not feed during molting which may take hours to a few days.

Tardigrades exhibit both sexual and asexual reproduction. Parthenogenetic strains are known where females produce females, without fertilization. For bisexual limno-terrestrial tardigrades, periods of reproduction occur quickly because of the erratic nature of cryptobiosis. Many tardigrades leave their eggs in their discarded skin when the molt. Others release their eggs free into the environment. Egg producing activity generally declines in the winter.

The egg may be smooth, have rounded projections, thin spines, or robust cones. Some projections are split or branched and the surface of the egg may be smooth, pitted, or patterned (Figures 4, 5). The size, shape, and pattern of the projections and the surface of the egg are the only known differences between some species of tardigrade, thus eggs are needed for identification.

The buccal apparatus of tardigrades show great variation in detail but great similarity in structure and function. Generally the mouth and buccal tube are flanked by two piercing stylets. A pharyngeal tube leads to the bulbus, sucking pharynx that opens into the alimentary system (Figures 7). Mouthparts are used in identification. The claws also show great diversity from simple, smooth sword-like to multi branched tree-like structures (Figures 8). They are heavily used in taxonomic determination.