Morphology of Hymenolepis spp.
The dwarf tapeworm, is the smallest cestode with an adult length of 15-44mm.
The rat tapeworm is a cestode of mainly rodents, adult length of 20-60 cm.
Round or slightly oval, size 70-86 um x 60-80 um, with striated outer membrane and a thin inner membrane. The space between the membranes is smooth or faintly granular. The oncosphere has six hooks.
Distinguished mainly by being typically larger, lacks polar filaments and has a yellow transparent cover.
Eggs are oval or subspehrical and smaller, ranging 40-60 um x 30-50 um. On the inner membrane are two poles, from which 4 to 8 polar filaments spread out between the two membranes. The oncosphere has six hooks. Notice in picture the extra detail of the two polar thickenings on the membrane of the oncosphere with filaments extending into the space around the hexacanth embryo.
H. nana developing in the small intestine of an experimentally infected mouse. (http://www.biosci.ohio-state.edu/~parasite/hymenolepis_nana.html)
Mature cysticercoids form infected beetles 20 days following infection. Dark area in each represents the invaginated scolex.
Whole H. nana adult worm with various stages of proglottid development stained for visibility. (http://www.biosci.ohio-state.edu/~parasite/hymenolepis_nana.html)
Scolex of H. nana has four suckers whch are not visible in this view, but one is marked by a *, and an armed rostellum that is clearly visible. The scolex of H. diminuta is similar but not armed with hooks. It has suckers. (http://www.biosci.ohio-state.edu/~parasite/hymenolepis_nana.html)