Trophozoites of Entamoeba histolytica/dispar. 

• (Reminder: in the absence of erythrophagocytosis, the pathogenic E. histolytica is morphologically indistinguishable from the nonpathogenic E. dispar!) 

Line drawing (A) and trichrome stain (B, C, D).  

Each trophozoite has a single nucleus, which has a centrally placed karyosome and uniformly distributed peripheral chromatin. 

• (This typical appearance of the nucleus is not always observed: some trophozoites can have nuclei with an eccentric karyosome and unevenly distributed peripheral chromatin.) 

• The cytoplasm has a granular or "ground-glass" appearance.  Entamoeba histolytica/dispar trophozoites measure usually 15 to 20 µm (range 10 to 60 µm), tending to be more elongated in diarrheal stool. 

(B:  specimen contributed by Dr. Ray Kaplan, SmithKline Beecham, Atlanta, GA.)

Courtesy of the Division of Parasitic Diseases at the National Center for Infectious Diseases, Centers for Disease Control and Prevension (public domain)

http://www.dpd.cdc.gov/DPDx/HTML/Amebiasis.htm