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Database Central
Wastewater Organisms Database
Water Bears (Tardigrades)
Purpose of Web Page
The purpose of this web page is to present the physical characteristics of water bears (Tardigrades). Water bears are large, in comparison to other wastewater organisms, usually about less than a mm. The majority of water bears are terrestrial forms that live in water film that sorrounds mosses and lichens. There are approximately 300-400 species, and the majority of these species are terrestrial, there are a few marine species that live in the interstitial spaces between sand grains. Water bears are not very good swimmers. They prefer to crawl along and cling to a substrate. Water bears have the capacity to shed or molt their skin and this is done 3-4 times during their lifetime. Water bears have two needle-like stylets (arrow is pointing at the stylet within its mouth) that they can protrude from their mouth and use for sucking the juices of plant cells. Some species of water bears suck the juices of nematodes, rotifers, and other small animals. Common American water bear species include Macrobiotus, Echiniscus, and Hypsibius. The majority of rotifers, specifically in some freshwater species, are parthenogenetic. Meaning that a male is not necessary for reproduction. One of the intriguing aspects of water bears is a condition known as cryptobiosis. Cryptobiosis is the capacity to go into a state of suspended animation. When harsh environmental conditions occur, such as a drought, a water bear is capable of reducing its body moisture content from 85% down to 3%. Under these condition, the water bear can withstand temperature extremes, ionizing radiation and oxygen defiency. They can remain cryptobiotic for years.
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This is a photograph of an exoskeleton or molted cuticle of a water bear. Within the cuticle lie a number of fertiled eggs. Photo was taken at a magnification of 100x. |
This photo of a water bear was taken at a magnification of 400x. Arrow is pointing at needle-like stylet. Muscles located next to the stylet are capable of protruding the piercing needle to the outside. |
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Date Page Last Revised: 14 April 2000
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