Hymenolepis nana causes dwarf tapeworm infection (hymenolepiasis).
The subspherical to spherical eggs have a thin hyaline shell measuring 30-47um in diameter and the six-hooked oncosphere is surrounded by a membrane that has two polar thickenings, from which arise four to eight filaments extending into the space between the embryo and the outer shell.
This egg is sometimes confused with that of Hymenolepis diminuta, the rat tapeworm which are much larger measuring 70-85um x 60-80um and the polar filaments are missing and can sometimes infect humans.
Invasion of Human Tissue by Cancer-Like Hymenolepis nana Cells Larry M. Baddour, MD Reviewing Muehlenbachs A et al., N Engl J Med 2015 Nov 4; 373:1845. Malignant transformation of H. nana in an immunocompromised host is suggested in this case report!
Photo: Hemant Sharma, 2014