A Giema stained slide from duodenal mucosa. The little dark creatures on top are parasites named Giardia. They can live without oxigen (anaerobic). To move around they have 4 pairs of flagellates. Accorinding to info on wiki Giardia were first described by the Antonie van Leeuwenhoek (a Dutch microscopist) in 1681. The genus is named after Alfred Mathieu Giard (a French zoonologist).

The parasites cause diarrhea, excess gas, stomach or abdominal cramps, upset stomach, and nausea. Giardia infections and is usually associated with poor hygiene and sanitation.