Giardia spp. are ___________ that live in their host's gastrointestinal tract.

• A. Flagellates
• B. Ciliates
• C. Apicomplexans
• D. Coccidians

Answer: (A)

Giardia species are flagellated protozoan parasites that inhabit the host’s small intestine. Their defining feature is the presence of multiple flagella, which is why they’re classified as flagellates. The other groups differ in characteristic motility and life style—they use cilia or lack flagella in their mature forms and are typically intracellular or non–flagellated—so they don’t fit Giardia’s locomotion or GI-tract lifestyle. Giardia attaches to the intestinal mucosa and can cause giardiasis, illustrating how the flagellated nature relates to both its movement and its ecological niche.