TABLE A11.

Morphology of the trophozoite and cyst forms of ciliates (Balantidium coli), coccidia, apicomplexa (Cryptosporidium), and Blastocystis spp.

Species	Stage	Size (μm)	Shape	Motility	No. of nuclei	Other features
Balantidium coli	Trophozoite	50–70 or more; usual range, 40–50	Ovoid with tapering anterior end	Rotary, boring	2 (1 large, kidney-shaped macronucleus and 1 small micronucleus immediately adjacent to the macronucleus; the macronucleus is occasionally visible in unstained preparations as a hyaline mass)	Body surface is covered by spiral, longitudinal rows of cilia; contractile vacuoles are present
	Cyst	45–65; usual range, 50–55	Spherical or oval		1 (large macronucleus visible in unstained preparations as a hyaline mass)	Macronucleus and contractile vacuole are visible in young cysts; in older cysts, internal structure appears granular
Cystoisospora belli	Oocyst	25–30; usual range, 28–30	Ellipsoidal	Nonmotile		Usual diagnostic stage is the immature oocyst with a single granular mass (zygote) within; the mature oocyst contains 2 sporocysts with 4 sporozoites each
Sarcocystis hominis	Sporocyst	13–17; usual range, 14–16	Oval	Nonmotile		Mature oocysts with a thin wall collapsed around 2 sporocysts or free fully mature sporocysts with 4 sporozoites inside are usually seen in feces
Sarcocystis suihominis	Sporocyst	1–15; usual range, 12–13	Oval	Nonmotile		Mature oocysts with a thin wall collapsed around 2 sporocysts or free fully mature sporocysts with 4 sporozoites inside are usually seen in feces
Cryptosporidium spp.	Oocyst	3–6; usual range, 4–5	Spherical or oval	Nonmotile		Mature oocysts contain 4 “naked” sporozoites; no sporocysts are present; oocysts are immediately infective
Cyclospora cayetanensis	Oocyst	8–10	Spherical	Nonmotile	May appear as “wrinkled” cellophane in stained preparations	Oocysts appear nonsporulated in clinical specimens; noninfectious
Blastocystis spp.	Vacuolated form	5–30; usual range, 8–10	Spherical, oval, or ellipsoidal	Nonmotile	1, usually, but 2–4 may be present (located in “rim” of cytoplasm; in binucleated organisms, the 2 nuclei may be at opposite poles; in quadrinucleated forms, the 4 nuclei are evenly spaced around the periphery of the cell)	Cell contains large central body, or “vacuole” with a thin band, or “rim” of cytoplasm around the periphery; occasionally a ring of granules may be seen in the cytoplasm; there are at least 10 subtypes, about half of which are pathogenic (morphologically the same); quantitate (rare, few, moderate, many, packed)