The

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

Heterotardigrada includes

tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ...

s (water bears) that have cephalic appendages and legs with four separate but similar digits or claws on each. 444 species have been described.

Anatomy

The anatomy of the reproductive system is an important defining feature in distinguishing the different groups of tardigrades. Heterotardigrades have gonoducts that open to the outside through a preanal gonopore, rather than opening into the rectum as in the only other confirmed class of tardigrades, the

Eutardigrada Eutardigrada are a class of tardigrades (Tardigrada) without lateral appendices. Primarily freshwater bound, some species have secondarily gained the ability to live in marine environments ('' Halobiotus''). By cryptobiosis many species are able ...

. The third class,

Mesotardigrada Mesotardigrada is one of three classes of tardigrades, consisting of a single species, ''Thermozodium esakii''. The animal reportedly has six claws of equal length at each foot. This species was described in 1937 by German zoologist Gilbert Rah ...

, is represented by a single species known from a single specimen that is now lost, and the location from which that specimen was collected has since been destroyed by an earthquake, so its reproductive anatomy has not been studied recently.

Ecology

Some

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

s of heterotardigrades are marine, others are terrestrial, but as for all tardigrades, all are aquatic in the sense that they must be surrounded by at least a film of moisture in order to be active – though they can survive in a dormant state if the habitat dries out.

References

External links

* * * {{Taxonbar, from=Q138557 Protostome classes Taxa named by Ernst Marcus (zoologist)