Which group has a digestive system with a mouth and anus?

• A. Rotifera
• B. Nematoda
• C. Both
• D. Neither

Answer: (A)

Having a mouth and an anus means a through-gut: a digestive tube with two openings that runs from the mouth to the anus, allowing one-way processing of food and the separate elimination of waste. Rotifers have this arrangement: food enters the mouth, is ground or processed in the pharynx, then passes through a gut to an anus at the rear. Nematodes also possess a complete digestive tract, with a mouth leading to a pharynx and intestine and ending at an anus. Because both groups have a through-gut with a mouth and an anus, the correct conclusion is that both Rotifera and Nematoda have a digestive system with a mouth and an anus.