Which tapeworm eggs feature an operculum at one end and a small terminal knob at the other end?

The correct answer is Diphyllobothrium latum, as it is well-known for its distinctive eggs that have an operculum at one end and a small terminal knob or projection at the opposite end. This morphological characteristic is a key identifier of the eggs of this species, which belongs to the family Diphyllobothriidae.

Diphyllobothrium latum eggs are typically found in fresh water and can be diagnosed through stool samples, teaching important aspects of tapeworm identification in parasitology. The presence of the operculum indicates the type of developmental stage and life cycle that these worms undergo, as operculated eggs are often associated with certain aquatic environments where the eggs need to hatch into larval forms.

The other choices represent different species of tapeworms whose eggs have distinct characteristics that do not include the operculum and terminal knob. For example, Taenia solium eggs are round and do not have an operculum, while Hymenolepis diminuta eggs are smaller, and Echinococcus granulosus eggs are also round but lack the operculum feature altogether. Understanding these morphological differences is crucial for proper identification and diagnosis of these worms in a clinical microbiology setting.