An amebic cyst 6-8 μm with four nuclei; name the species.

• A. Entamoeba hartmanni
• B. Endolimax nana
• C. Entamoeba histolytica
• D. Entamoeba coli

Answer: (A)

The key idea is using cyst size and nuclear count to tell Entamoeba species apart. A mature amebic cyst with four nuclei that measures about 6–8 micrometers fits best with Entamoeba hartmanni. This species is the smallest Entamoeba group and is defined by such small cysts with four nuclei. In contrast, Entamoeba histolytica cysts are larger (around 10–20 μm) even though they also have four nuclei; Entamoeba coli cysts are larger still and often have more than four nuclei; Endolimax nana cysts can be very small as well but are distinguished by other nuclear features rather than this precise size range. So, the description most characteristic of Entamoeba hartmanni.