While comparing invertebrate groups, a worm has a fluid-filled cavity fully lined by mesoderm and divided by septa. The feature being tested is:

Annelids are coelomate animals. Their true coelom is lined by mesoderm and often partitioned by septa, supporting movement as a hydrostatic skeleton. This MCQ belongs to the Annelida topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.