Alimentary canal is not found in

• Cestodes belong to phylum Platyhelminthes
• These have incomplete digestive system
• One of the main features of the cestodes is absence of digestive tract that means absence of alimentary canal. 
• Under the flatworm network of species, Cestoda falls. 
• There isn't  any mouth or buccal hollow space for this network of species. 
• They have tubes wherein the vitamins from the host 's alimentary canal are ingested.
• Now the arthropods are Decapoda and Arachnida. 
• They have an alimentary canal including the 'oesophagus and stomach'. 
• There are numerous arthropods with underdeveloped meals ducts.
• Apoda, on the alternative hand , comes beneath the chordates and has a pretty evolved alimentary canal.

Hence, option D is the  correct answer.