In this particular view, a microorganism is featured, the exterior of which is covered by numerous projections imparting an appearance of a sea urchin. This microscopic “pin cushion” was teathered to its surroundings by a biofilm within which many bacteria, and amoeboid protozoa could be seen enmeshed as well. Though many organisms found in untreated waters are harmless, there are many that are pathogenic to both humans and animals, including Giardia spp., free-living amebae, and E. coli just to name a few. (Image Credit: Public Health Image Library)