Alimentary canal is absent in

Explanation

• Alimentary canal is a long tube of organs that runs from mouth to the anus, which is absent in Taenia and Echinococcus.
• Taenia (tapeworm) and Echinococcus (dog tapeworm) belong to phylum Platyhelminthes are both endoparasites and possess hooks and suckers.
• They lack an alimentary canal as they absorb digested food directly from the host small intestine through their body surface. 
• Ascaris (Roundworm) belongs to phylum Aschelminthes, most common endoparasite of humans, possesses a complete alimentary canal.
• Fasciola is also an endoparasite that lives in the sheep's liver and has an incomplete alimentary canal as it lacks anus.

Final Answer

Hence the correct option is C i.e., Taenia and Echinococcus.