The correct answer is A) is self-desludging. The key difference between the centrifuge bowl shown in the illustration and a traditional tubular bowl is that the illustrated unit has a self-desludging design. This means that the solids (sludge) are automatically discharged from the bowl during operation, without the need for a separate discharge ring. This is a more efficient and convenient design compared to the older tubular bowl type, which would require manual intervention to remove the accumulated sludge. The other options are incorrect because they do not accurately describe the primary difference between the two bowl designs. The rotational speed of the bowls is not specified in the question, and the lack of a discharge ring is a feature of the self-desludging design, not a separate requirement.