Which of the following body characteristics distinguishes Ascaris from Earthworms?

Analyze the question: We are asked for a body feature that sets Ascaris (a roundworm, Phylum Nematoda) apart from the earthworm (Phylum Annelida).

Concept: The main difference between these two worm groups is body segmentation.

• Annelids (earthworms): The body is divided into many ring-like segments (metameric segmentation). The rings are visible on the outside.
• Nematodes (Ascaris): The body is long, cylindrical, and tapered at both ends. It is unsegmented and covered by a tough cuticle.

Checking each option:

• A. Bilaterally symmetrical: Both animals are bilaterally symmetrical, so this doesn't distinguish them.
• B. Cylindrical: Both have roughly cylindrical bodies, so this doesn't distinguish them.
• C. Segmented: This is true of the earthworm only. It would be a wrong description of Ascaris.
• D. Soft: Both have soft bodies, so this doesn't distinguish them.
• E. Unsegmented: This is true of Ascaris and not of the earthworm, so it is the distinguishing feature.

Answer: The body of Ascaris is unsegmented, while the earthworm's body is segmented.

Exam tip: For "distinguishing feature" questions, eliminate every characteristic shared by both organisms. Remember: Nematodes = No segments; Annelids = Annular rings.