Answer: This is a copepod, a microscopic crustacean found in both fresh and salt water habitats. Cyclops, (shown here) is one of the most common genera of freshwater copepods. One reader had mentioned that Diaptomus could also be considered. This copepod has a very similar appearance to Cyclops, but has antennae that are longer than their body.
Copepods play a role in the live cycle of several parasites, including Dracunulus medinensis and Spirometra, Gnathostoma and Diphyllobothrium species. Of note, the very first case that I ever posted on this blog was a copepod containing D. medinensis larvae! You can see it HERE.
Henry Bishop of the CDC DPDx team was kind enough to provide the following images of copepods infected with D. medinensis larvae. The second photo was taken after gentle manipulation which allowed for expression of a larva.