For semester exam preparation, consider this situation: a worm from soil is cylindrical, unsegmented, and has a fluid-filled cavity not fully lined by mesoderm. The correct conclusion is:

Nematodes are pseudocoelomate roundworms. Their body cavity acts as a hydrostatic skeleton and their cylindrical unsegmented form distinguishes them from flatworms and annelids. This MCQ belongs to the Nematoda topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.