Upon close inspection of movement in annelids and nematodes, you would notice an obvious difference. Nematodes tend to wriggle back and forth, while annelids tend to contract along their length as their girth swells and then thins out as they stretch. What anatomical feature explains this type of movement?

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Quizplus · Accepted Answer

Nematodes lack circular muscle fibers, which is why they can only move in a wriggling motion using their longitudinal muscles, unlike annelids that have both circular and longitudinal muscles allowing for more complex movement.

Upon Close Inspection of Movement in Annelids and Nematodes, You