Answer to Case 58
The organism shown was Retortamonas intestinalis, a flagellate that has been found in the intestinal tract of humans.  Diagnostic features observed were:

• Cysts of R. intestinalis are usually ovoid or pyriform in shape and range from five to seven micrometers in diameter.  Cysts of Chilomastix mesnili have a similar morphology, but are slightly larger (seven to ten micrometers).
• Cysts of R. intestinalis are uninucleate with a compact central karyosome and varying amounts of peripheral chromatin.
• Fibrils (associated with the cytostome) were seen in some of the cysts.
• Trophozoites of R. intestinalis are usually ovoid or pyriform but can be somewhat elongated.  Normal size range is five to ten micrometers long.  Trophozoites of C. mesnili are normally 10 to 15 micrometers in length.
• Presence of a cytostome at the anterior end that can extend one half the length of the organism.