Which of the following is NOT an annelid?

• A. Earthworms
• B. Leech
• C. Nematodes
• D. Nereis

Answer: (C)

Annelids are segmented worms with true repetition of body units, a true coelom that runs through the segments, and often specialized structures on each segment. Earthworms are the classic example of segmented annelids, showing clear metamerism. Leech is another annelid, even though some species lack visible bristles, they still have true segmentation. Nereis is a polychaete annelid with many segments and paired appendages on those segments, illustrating the same metameric pattern.

Nematodes, on the other hand, are roundworms that do not have true segmentation and possess a pseudocoelom rather than a true coelom. Their bodies are unsegmented, and their structural plan is simpler than that of annelids. Because they lack the characteristic segmentation and coelomic organization of annelids, nematodes are not part of that group.