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Daphnia is a tiny crustacean that lives in lakes and ponds. It is increasingly being used as an environmental sensor -- to help scientists determine changes in water salinity, temperature, even the presence of predators and toxins. Behind the organism's main eye (black) are the gut diverticula (green), which are particularly sensitive to the presence of certain environmental toxins, and change visibly in form. Scientists are also using genomic and proteomic techniques to determine how Daphnia respond to external changes.
