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[Dientamoeba fragilis]

Dientamoeba fragilis is a flagellate that must be morphologically differentiated from the small nonpathogenic amebas.  Dientamoeba fragilis has no cyst stage, and its trophozoites measure 5 to 15 µm.  The flagella is not usually evident and the pseudopodia are angular to broad-lobed and transparent.  While most trophozoites are typically binucleate, some have only one nucleus.

A	B

A, B: Binucleate forms of trophozoites of D. fragilis, stained with trichrome.

C	D

C, D:  Binucleate forms of trophozoites of D. fragilis, stained with trichrome.

E	F

E:  Binucleate form of a trophozoite of D. fragilis, stained with trichrome.
F:  Binucleate form of a trophozoite of D. fragilis, stained with trichrome.  A cyst-like form of Blastocystis hominis lies to the left of the D. fragilis.