Incomplete alimentary canal occurs in
A) Fasciola
B) Ascaris
C) Wuchereria
D) Rhabditis

Hint: It is a tube of muscle that can be extended through the mouth to anus. In the right option, the digestive system starts with the mouth but does not end to anus so it is termed as incomplete.

Complete Answer:
A) Fasciola possesses an alimentary canal which does not end at anus. At the anterior position of their body, the mouth is placed and it is surrounded by a sucker of oral rib. After mouth, pharynx and then oesophagus is placed. The pharynx is ovoid in structure. These two are with a cuticle that are lined internally. Endodermal epithelial cells line the intestine.

B) The canal system of Ascaris contains two canal systems that are longitudinally lateral in structure. It is also called the left and right canal system. A canalicular network connects the canals in anterior position. It is transversely arranged. Every canal is extended at their posterior end and the both ends are closed.

C) The alimentary canal system of Wuchereria is divided into several segments. They are capsules of stoma or buccas, muscular and glandular esophagus, some intestinal valves etc. Several nutrients are broken down by the function of bancrofti.

D) The alimentary canal of Rhabditis contains some specialized organs that are digestive also and contain some external openings. The canal system contains mouth, intestine, pharynx, rectum and lastly anus. It ends at the anus adjacent to the tail.

Hence Option A: Fasciola is the correct answer.

Note: Incomplete alimentary canal is the canal system which starts from the mouth but does not end at the anus. Hence Fasciola has this feature that's why it is the correct answer.