Ascaris lumbricoides is best described as which of the following?

Ascaris lumbricoides is best described as which of the following?

• A. A large intestinal roundworm.
• B. A protozoan parasite.
• C. A cestode.
• D. A trematode.

Answer: (A)

Ascaris lumbricoides is a nematode, a roundworm that lives in the human small intestine as an adult. It is a large, elongated, nonsegmented worm, which distinguishes it from tapeworms (cestodes) that are flat and segmented and from flukes (trematodes) which are leaf-shaped. Protozoan parasites are single-celled organisms, not worm-like. Thus, the description that fits best is a large intestinal roundworm.

Ascaris lumbricoides is a nematode, a roundworm that lives in the human small intestine as an adult. It is a large, elongated, nonsegmented worm, which distinguishes it from tapeworms (cestodes) that are flat and segmented and from flukes (trematodes) which are leaf-shaped. Protozoan parasites are single-celled organisms, not worm-like. Thus, the description that fits best is a large intestinal roundworm.