Focus on Giardia lamblia

These are flagellated unicellular diplomonad (indicates "two separate haploid - n vs. diploid, 2n - nuclei") eukaryotes lacking mitochondria and plastids.  Giardia, which tend to infect the human intestine, also have simple cytoskeletons.  These things indicate Giardia is the closest living organism to the beginning of the model of endosymbiosis.

Fact Sheet:

1. 2 nuclei, each with a set of chromosomes; together the organism actually is a diploid.
2. unicellular
3. no mitochondria or plastids (pigmented organelles located in the cytoplasm)
4. a simple cytoskeleton

Next:  "Protozoa."