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According to the book Guide to Microlife by Kenneth G. Reinis and Bruce J. Russel the above image is a cladoceran or in other words a water flea.

According to the book Guide to Microlife by Kenneth G. Reinis and Bruce J. Russel the organism above is a lecane.

According to the book Free-Living Freshwater Protozoa by DJ Patterson the organism pictured above is a tachysoma.

According to the book Guide to Microlife by Kenneth G. Reinis and Bruce J. Russel the above organism is an ostracoda or in other words a seed shrimp.