The Cladoceran reference article from the English Wikipedia on 24-Apr-2004
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Cladoceran

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Cladocera or Cladocerans are small crustaceans, part of the class Brachiopoda. They form a monophyletic group, which is currently divided into 4 suborders, 11 families, 80 genera, and about 400 species. The most commonly known genus is Daphnia (freshwater water fleas)), which is the most researched in this group.

Daphnia are commonly used to test the toxicity of chemicals in solution or for water pollution.