TABLE A8.

Morphology of cyst forms of amoebae

Species	Size (diam or length [μm])	Shape	Nucleus characteristic(s)			Cytoplasm characteristic(s)
			No.	Peripheral chromatin	Nuclear chromatin	Inclusions	Appearance
Entamoeba histolytica/E. dispar	10–20; usual range, 12–15	Usually spherical	4 in mature cyst; occasionally 1 or 2 in immature cysts	Peripheral chromatin present; fine, uniform granules, evenly distributed	Small, discrete, usually centrally located	Present; elongated bars with bluntly rounded ends	Usually diffuse; concentrated mass often present in young cysts; stains reddish brown with iodine
Entamoeba hartmanni	5–10; usual range, 6–8	Usually spherical	4 in mature cyst; 1 or 2 often seen in immature cysts	Similar to E. histolytica	Similar to E. histolytica	Present; elongated bars with bluntly rounded ends	Similar to E. histolytica
Entamoeba coli	10–35; usual range, 15–25	Usually spherical; occasionally oval, triangular, or other shapes	8 in mature cysts; 16 or more are occasionally seen in supernucleated cysts; 2 or more are occasionally seen in immature cysts	Peripheral chromatin present; coarse granules are irregular in size and distribution but often appear more uniform than in trophozoites	Large, discrete, usually eccentric but occasionally centrally located	Present, but less frequently seen than in E. histolytica; usually splinter-like with pointed ends	Usually diffuse, but occasionally there is a well-defined mass in immature cysts; stain reddish brown with iodine
Entamoeba polecki	9–18; usual range, 11–15	Spherical or oval	1, rarely 2; occasionally visible in unstained preparations	Usually fine granules that are evenly distributed	Usually small and eccentric	Present; many small bodies with angular or pointed ends or a few large ones; may be oval, rod-like, or irregular	Usually small, diffuse masses stain reddish brown with iodine; a dark area called an “inclusion mass” (possibly concentrated cytoplasm) is often also present; mass stains lightly with iodine
Endolimax nana	5–10; usual range, 6–8	Usually oval, may be round	4 in mature cyst; immature cysts, 2, very rarely seen and may resemble cysts of Enteromonas hominis	None	Large (blot-like), usually central	Occasionally granules or small oval masses are seen, but bodies as seen in Entamoeba spp. are not present	Usually diffuse; a concentrated mass is seen occasionally in young cysts; stains reddish brown with iodine
Iodamoeba bütschlii	5–20; usual range, 10–12	Ovoidal, ellipsoidal, triangular, or other shapes	1 in mature cysts	None	Large, usually eccentric; refractile, achromatic granules on one side of the karyosome; indistinct in iodine preparations	Occasionally granules are present, but chromatoid bodies as seen in Entamoeba spp. are not present	Compact, well-defined mass; stains dark brown with iodine