Final answer:
The protozoan that presents a blue halo under ultraviolet fluorescence microscopy is Cyclospora cayetanensis. Additionally, Trypanosoma brucei is known for evading the host immune system by altering its surface proteins with each generation.
Step-by-step explanation:
When using ultraviolet fluorescence microscopy, the protozoan Cyclospora cayetanensis exhibits a distinct blue halo. This is due to the protozoan's autofluorescence characteristics, which allow it to emit light and are useful in identifying the organism. This autofluorescence makes Cyclospora cayetanensis distinguishable from other protozoans under UV light.
Protozoan Surface Protein Alteration to Evade Host Immune System
Among the protozoans known for altering their surface proteins to evade the host's immune system, Trypanosoma brucei is notable. This mechanism allows the parasite to persist within the host by avoiding detection and destruction by the immune system. This capability for antigenic variation contributes significantly to the parasitic protist's pathogenicity.