Which parasite is a cestode?

• A. Dirofilaria immitis
• B. Otodectes cynotis
• C. Dipylidium caninum
• D. Fasciola hepatica

Answer: (C)

Cestodes are tapeworms—long, flat, and segmented worms that attach to the intestinal wall with a scolex and release egg-containing proglottids. Dipylidium caninum is a common tapeworm in dogs and cats and is classified as a cestode. It often uses fleas or lice as intermediate hosts; when the definitive host ingests an infected flea, the tapeworm develops and can shed rice-grain–like proglottids. Clinically you might see these small, white packets in the stool or around the animal’s anus.

The other organisms listed are not cestodes: Dirofilaria immitis is a nematode (roundworm) causing heartworm; Otodectes cynotis is an arachnid (ear mite); Fasciola hepatica is a trematode (liver fluke) with a different life cycle and morphology.