| Scientific classification |
|---|
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| Families |
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Order Arthrotardigrada
Archechiniscidae
Batillipedidae
Coronarctidae
Halechiniscidae
Renaudarctidae
Stygarctidae
Order Echiniscoidea
Echiniscidae
Echiniscoididae
Oreellidae
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The class Heterotardigrada includes tardigrades (water bears) that have cephalic appendages and legs with four separate but similar digits and/or claws on each.
The anatomy of the reproductive system is an important defining feature in distinguishing 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 (the third class Mesotardigrada, is represented by a single species whose reference material was destroyed in an earthquake, so its reproductive anatomy has not been studied recently).
Some orders 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.
Reference
http://www.itis.usda.gov
TSN: 155167
TSN (Arthrotardigrada): 155168
TSN (Echiniscoidea): 155299
