TABLE A7.

Morphology of trophozoite forms of amoebae

Species	Size (length [μm])	Motility	Nucleus characteristic(s)			Cytoplasm characteristic(s)
			No.	Peripheral chromatin	Nuclear chromatin	Appearance	Inclusions
Entamoeba histolytica/E. dispar (E. histolytica is the true pathogen, and E. dispar is nonpathogenic)	10–60; usual range, 15–20 (commensal form) and over 20 (invasive form)	Progressive, with hyaline, finger-like pseudopods	1 (not visible in unstained preparations)	Fine granules; usually evenly distributed and uniform in size	Small, discrete; usually centrally located but occasionally eccentric	Finely granular	RBCs occasionally; noninvasive organisms may contain bacteria; no RBCs seen in E. dispar
Entamoeba hartmanni	5–12; usual range, 8–10	Usually nonprogressive but may occasionally be progressive	1 (not visible in unstained preparations)	Similar to E. histolytica	Small, discrete, often eccentric	Finely granular	Bacteria
Entamoeba coli	15–50; usual range, 20–25	Sluggish, nonprogressive, with blunt pseudopods	1 (often visible in unstained preparations)	Coarse granules, irregular in size and distribution	Large, discrete, usually eccentric	Coarse, often vacuolated	Bacteria, yeasts, or other materials
Entamoeba polecki	10–25; usual range, 15–20	Usually sluggish, similar to E. coli; occasionally, in diarrheic specimens, motility may be progressive	1 (may be slightly visible in unstained preparations; occasionally may be irregularly distorted by pressure from vacuoles in cytoplasm)	Usually fine granules are evenly distributed; occasionally granules may be irregularly arranged; chromatin sometimes in plaques or crescents	Small, discrete, eccentric; occasionally large, diffuse, or irregular	Coarsely granular; may resemble E. coli; contains numerous vacuoles	Bacteria, yeasts
Endolimax nana	6–12; usual range, 8–10	Sluggish, usually nonprogressive with blunt pseudopods	1 (visible occasionally in unstained preparations)	None	Large, irregularly shaped, blot-like	Granular, vacuolated	Bacteria
Iodamoeba bütschlii	8–20; usual range, 12–15	Sluggish, usually nonprogressive	1 (not usually visible in unstained preparations)	None	Large, usually central; surrounded by refractile, achromatic granules; these granules are often not distinct even in stained slides	Coarsely granular, vacuolated	Bacteria, yeasts, or other materials
Dientamoeba fragilis	5–15, usual range, 9–12	Pseudopods are angular, serrated, or broad lobed and hyaline, almost transparent	2 (in ∼20% of organisms, only 1 nucleus is present; nuclei are invisible in unstained preparations)	None	Large cluster of 4–8 granules (tetrad)	Finely granular	Bacteria